This dynamic is really common. We have it in our system too. It's a current focus for us in healing.

Our T explains it to us like this: In childhood, it was necessary for one or some of the alters to be positively attached to the abusers. We had to eat breakfast with them every morning, no matter what went on in the night time. There needed to be some part of self who was able to do that, to sit down with them and smile and appear like everything was okay.
And T is right, that is how it was for us. Our father became very violent and abusive if he didn't think we were displaying the respect and adoration he felt he was due. We absolutely needed to have parts of self that could smile at him and respect him and play that part when it was needed. If we weren't able to do that, he would have exploded in rage and abused us more.
For us, the only way those parts could do that job was if they didn't know anything at all about the abuse. They had to have no knowledge of any type of abuse at all. The only father they saw was when he was being "normal" and "socially acceptable" and non-abusive. One alter in particular still believes that no abuse occurred and any parts that believe it did are lying and deceitful and horribly awfully ungrateful for all the "wonderful things" the father did.

I understand the way for us to heal this rift in us is for the one(s) who only know the "good" father to learn about the abuse, and for the ones who only know the abusive father to develop an understanding for the reasons why it was important for some alters to not know about it, for whatever reason it served the developing child at the time.
It's hard. It's definitely not an easy process and there is a lot of resistance on both sides. It seems to be easier for us to first develop our understanding, compassion and gratitude for the ones who helped reduce the amount of overall abuse by "not knowing" and being able to act as though nothing was wrong. That was such an important job that saved us a lot of extra suffering. We can see that it also enabled the "overall child" that we were to experience some times of "normality", like just sitting down and eating breakfast with the family without being aware of the overall terror that was our life.

What really isn't helpful for us is just asking our system who deals with what and then trusting them to do their job, because in us that just serves to maintain the separation and dysfunctional ways of relating to the world. The dissociative dynamic that enabled one part of us to eat breakfast with the family (just as one example of action - there were many more) served it purpose back then but is not appropriate in our life today. Now we are adult and we want to learn to do things differently, as it seems you do.

So we are learning that the job of the alters who were/are positively attached to the abusers was actually protective. In childhood, for us, it helped reduce the overall amount of abuse we received and also allowed us to experience some aspects of "normality". The more we think about it the more we see this to be true.

Every part is there only for a very, very good reason. If they didn't help in some way, they just wouldn't be. Sometimes it appears as though they hurt rather than help but in the end every single part is a helper. Even Star, even if you are not sure how just yet.