Hello HelplessSis: I see this is your first post here on PC. So... welcome to Psych Central. I'm sorry you & your parents are having so much difficulty with your brother. I do agree that your parents need to figure out a way to stop enabling him. Here are links to 10 articles, from Psych Central's archives, on the subjects of thinking (or perhaps hoping) you can change others as well as on establishing boundaries. Perhaps some of these may be articles you could share with your parents too?:

You Can Only Change Yourself

Stop Trying to Change People Who Don't Want to Change | Happily Imperfect

When You Want to Change a Loved One

How You Can Help Too Much/Psychology of Women | Psychology of Women

How to Stop Enabling | Happily Imperfect

What Are Personal Boundaries? How Do I Get Some?

https://psychcentral.com/blog/the-7-laws-of-boundaries/

https://psychcentral.com/lib/tips-on...relationships/

https://psychcentral.com/lib/why-boundaries-dont-work/

https://blogs.psychcentral.com/imper...ur-boundaries/

I hope you find PC to be of benefit.