Has she lost her mental capacity? Urgent advice needed. Thanks

I am facing a very hard situation and I am trying to find some info. I posted on other forum but did not have enough replies so I found this forum and I am posting here. I really need information and advice.

First I completely understand that no one can give a diagnosis based on the comments here and it has to be face to face with the patient.

What is needed: I want to know if there is any strong indication that my mom has lost her mental capacity: -What are the indications or pointers that I need to look out for? -when is it not normal for someone to talk to themselves? . I am doing this so I can legally manage the financial and medical help for her. To remove her from decisions making process.
Please read now:
In summary:
My parents married: dad around 21-22 yrs mom around 16 or 17yrs.
Dad from limited income family (not sure if i can say poor).
Dad joined the military forces and stayed in service until he reached around 45yrs old and reached a high rank Brigadier general and then worked in several private companies. Highest education technical diploma (less than university) and many courses throughout his career in the military.
Mom was a house wife with highest education is high school, she barely passed her high school. (Don't get me wrong that there are people who did not go to school and are very successful in life, life is the best school is one learns from life). Her family was from a good income family.
They did not get along. They always fought and both are stubborn (due to their relationship). My father was a hard man towards us (3 children all male). He used to beat us and was very hard. I disliked that in my life but accepted it. We grew into it. We lived in housing complex which limited our interaction with other public (military basis).
Dad and mom never connected and we did not feel connected with Dad. Mom made sure of it. She always said negative things about dad and his side of the family.
Mom always put down dad and saying he was a bad man and telling us stories of how hard and insensitive he was towards her and his social dealings with other people, giving examples.
Dad was controlling person in every way.
After a life together of 23 years, the conflict between grew worse and it reached to a point when dad used to hit mom, this did not happen before and I defended my mom by hitting dad (only happened once).
my other brothers are troublesome children: always fights at school and getting in trouble. The did not get good grades in school.
I am the quite one in the children, never been to fights and did good in school, I used to concentrate on what I want to go for, and disregard everything else, I followed a rule: if it will hurt me run away from it and if it helps run to it (in simple terms), others made fun of me at school, and I did not answer back, so you can say I was the joke of the class. In rare cases I stood up to them, as knowing that it will lead to a fight and it will hurt me so that is why I let it go most of the time, so being scared was not the reason for me not standing up to them. I had few close friends that I can rely on during my life, none ever knew the truth of the house but had an idea.
Ever since I started to become aware over the age of 10yrs, I noticed mom used to talk to herself and now it happens often. My dad passed away and I stayed to deal with the matters. I am a mature person: above 40yrs of age.
Since then my contact with mom was more as I needed to take care of the matters. I noticed her thinking (which is not sound). Her talking to herself has become more often and sometimes when we have visitors, when she goes to get tea or coffee people can hear her talking to herself. I noticed that she did not take proper decisions and she threatened me in several ways as we had disagreement about couple things, this should not come to this, one of the threats is that she will deny me from inheritance, and other threat is to kick me out of the house. The disagreement was due to her taking wrong decisions on matters which she did not understand and she thinks is correct and never wrong and she was dead wrong (can’t go into specifics but she was wrong otherwise I would not do the correct thing). We always fought for no reason at all.
I am drawing a bad picture towards my dad, I know but things changed when I started noticing bad vibe from mom (after my father passed away RIP). One time she had a visitor and I heard her say that she used to wash my brothers face with cold water when he was about 2yrs old so he does not sleep in order she can go to club. This made me notice more and think about other things happened in my life.
I did apologise to my dad for hitting him at that time but to tell the truth it was not from my heart I said it to get things rolling as you can say. But now I began to understand why dad acted the way he acted: he was hard on us because mom was not taking responsibility and if he did not do it, we would be lost. As I did hit him, he forgave me and paid for my university and other higher qualification. Which he could have said to me University is enough and get yourself sorted. If he was a bad and selfish man, he would have left the family. He would not have stuck around with all this hellhole. He sacrificed his life to us (his children) and mom never ever appreciated that. My father passed away and I found all this out after he was dead, and now there is nothing I can do to amend things with him. It is too late and I am not able to think straight and I don’t concentrate in work and make big mistakes.
He used to say he did not want children when we were kids and that hurt me, but now I know why he said it, because of the reason I stated above. It was because my mom did not take responsibility.
Before anyone says I'm a gold digger and want the money from her, understand where I'm coming from. Dad left everything to her we have couple of lands and houses, one which is rented out.
I had a fight with one of my brothers which led me to report him to police but then withdrew it as I did not want more trouble. Mom never ever tried to mend things between us, this all happened after my father's death. She kept away from this subject.
My brother is other story to himself, he is irresponsible and does not care and caused me and my other brother a lot of problems.
My Moms lies to me in important things in life. The people who rent the house are damaging the house and treating it like their own. She does not want me to interfere in any aspect and the renters are taking a lot of advantage of this. Very low rent and damaging the property. the property will need fixing and the cost will be more than the rent received.
She favors one child over us, the other two.
I have started recording her by camera as I need proof, some of the things I found out:
- she lies to me for major or import matters,
- she tell lies to her friend about me, how I act while other sons are better,
- she said that if sons from other religion would have been better than us (talking to herself).
- she indicated that if her sons were from the other religion would have been better to her friend (going outside of the family and making it public),
- she complains about us to her siblings (all grownup and have their families). Also, they are not helping as all my life they also stated my father was bad.

I put my life on hold to help the family and I got beaten up by my brother for stupid reason, while he did nothing.
I am not able to concentrate at work or I don't have any feeling in anything, even that is from long time ago, but now I managed to pinpoint all the issues and now I am certain my dad was not a bad or selfish man at all, what he did was the right thing and did it to protect us (his children), if he was a bad and selfish man, he would have left the hellhole we are in and got divorced.
Several points to state: cultural aspects do have effect in our lives, now more relaxed but I am referring to my parent’s era. We are all in the same religion. My brother is a careless and selfish person and he is trying to get his hands on some of the inheritance, I heard my mom telling others that he asked her to sell couple of properties.

I went for consultation with a physiologist (giving false names) and I paid money for the consultation.
I want to know if there are indications that my mom lost her mental capacity so I am able to remove her power of authority over our properties as she is planning to do something will hurt me and my other brother.
Finally, there are things which I have not stated here. that will give more indication to my conclusion above.

I am sure all of you know this is a very sensitive issue and hell will break lose if anyone finds out what I am planning to do.
I have more than 50 hours of video recording of her (including some with her friend) showing her talking and screaming sometimes to herself. and few hours talking to her friends (stating what I wrote above), also, she like to go for a walk outside and she talks to herself while she is walking alone.

My life is in shatters now, I am not able to sleep one whole night and don't feel like eating right, although I do try.
Finally thank you for taking the time to read this and I appreciate sound and good advice. I am aware that no one can give a diagnose here until meeting with the person face to face, but I need to know if there are strong indications that my mom has lost her mental capacity.
(sorry if there are any spelling or missing words as typing is slower than thinking).

If you can get her into a nero-psychiatrist that'll be your best bet. I would consult a lawyer to find out the steps you have to take.

Contact a lawyer to see what steps you may need to take. When it comes to inheritances family members can do very selfish things like try and gain an advantage. It's hard to protect people from making bad decisions.

If you eventually get down to having power of attorney you may like to share it with another family member.

it is like impossible to get someone declared insane and your mom is no where near that. just look at all of the mentally ill walking around nyc these days they all have family who want them put away and helped but it don't go like that ever if she sees you taping her, she will look at you as the "enemy" or mentally ill one. and end up screwing you into the ground.all while your bonehead brother comes out looking good. do just as your mother says and try to get her to like you......you never know? if she likes you everybody may get along again... remember... piss her off and you will pay.. no doubt-about it.

thanks for your replies. for the first two, I already saw a lawyer and was advised to obtain a letter from that she lost her mental capacity.
For the third reply, I am not able to sit down and do as she wants, she is driving us to the ground. I have other info which I have not posted here, as it will take too long and will identify her, if by chance anyone who knows us reads this.
Before I start this process, I like to know what can I look such as signs or behavior issues that will give me strong indications that she lost her mental capacity, so to get comfort to start the process. I can not sit down and watch what is happening, she has destroyed our family and our lives. I don't care what will happen, I will do what ever it takes, my life is in shatters now because of her mental state. I have other evidence to show how ill heart she is too. I hope someone who know what I should look out for can write something. this would be great help. I am aware that no one can diagnose based on this or even give an accurate response, so I am not looking for an assessment about her situation here. Thanks all for your help.

I like to add that my mother is over 70years old. The situation that I wrote about, is from long time ago. It is not just happening recent.
It will be hard to explain that how my life was, but it was a sheltered life and we had it hard and I am the type of person who wants to make (build) himself. I do not want to be just a regular guy (not intended to insult anyone- what I mean i don't want just a bachelor degree only, I want higher education, I want to improve on myself, this is what I mean), so I was busy with my studies and worked hard and kept out of trouble and when others made fun of me, my response is to be quite and not tackle them as my thinking was it lead to more trouble and then I will lose time from studying etc... and at the end i would lose, this was my point of view.
My mom was the same mentality since I became aware, she talked to herself as if someone is with her, she did not take motherly responsibility for us. She used to let my younger brother do what he want against the instruction of my father (when he was at work) when I always told her that she stand beside my father and instruct my younger brother to do as requested. There are lots of things like that.
I am hoping for someone to write what signs or things I should look out for that can give indication that she lost her mental capacity.
Also, I read on the web that when someone is talking to themselves its normal, so what is the line between normal and not normal? This is what I want to know or find out. For myself, when I am working (or before studying), I used to ask aloud the questions in my mind (especially when working in an open area where there are distractions), this method helped me to concentrate on what I am doing, but I do not answer myself as if I am in a dialog with myself, my mom talks to herself as if there is someone next to her and answering back. I suspect this is not normal, but I like to know if I am correct or not. Thanks to anyone who provides comments,