How do I deal with finding out my parents abused my sister?

I've always gotten along with my parents pretty well, I have a lot of siblings (8 others besides me) but they did a pretty good job raising me. I'm currently 16 and still living with them.
My oldest sister and my parents have always had a bad relationship for as long as I can remember, some of my youngest memories were of them screaming at each other and her having emotional breakdowns time and time again. Like literal breakdowns of just hysterically crying and screaming I HATE YOU over and over, for things that don't seem big at all. And as a child I always thought she was just being an over emotional brat, that's what I've thought for a long time.
Couple days ago she came over ( she does every couple of weeks) and after all the other siblings left it was just the 2 of us. I have no idea how the topic even came up but we ended up talking from midnight to 6 am about her childhood and the things my parents did to **** her up. Shes always been rebellious and kind of a little **** but jesus christ the way they treated her was just inhuman. She was grounded almost her whole youth they used to ground her a week for every minute she was late. They told her to leave one day when she was 17 and then called her in as a runaway and when she got sent to juvie a while later they left her there for almost a month. Like a kid that poses no danger what so ever to you and you treat them like a annoying pet getting sent to the pound. They never even got her out it was her friends parents that somehow somehow worked it out. My dad has always had anger issues but it mostly manifests in him flipping out and yelling when too many people are in the kitchen or something stupid like that, but to her he could be physically abusive like shoving against walls mostly but the worst of it was him banging her head against a table in rage. And something that broke my heart to hear was that it him doing that hurt less then my mom seeing him do it and not say anything.
I've been doing a lot of analyzing since that night and thinking back I realise what a toxic pair my parents did and still do make. My dad is this narcissistic, overly confident, smart when it comes to somethings but thinks that makes him smart at all, things type guy. Super sarcastic, always putting his word in type. My mom is this very submissive, passive, catholic woman who cannot seem to stand up for herself when it comes to him. Most their interactions seem to be him putting her down and her not knowing how to stick up for herself. The only thing they truly seem to have in common is their mutual hatred for my sister. Like whenever her name comes up some snarky comment by them always follows.
I think what bothers me the most is that it isn't a story of 2 flawed people poorly raising a child only to realise their mistakes and try to undo the damage they did to her, its 2 flawed people doing a bad job raising their kid then quitting and trying to just do better with their other kids instead of rectifying the mistakes they made. They still treat her extremely poorly and I'm embarrassed it took me so long to see my sister wasn't the bad guy.
There's a lot of details I left out but you get the picture. Do you think there is anything that can be done to rectify or repair their relationship? Should I just straight up call them out? Idk if anybody actually read through this but if you did thank you and it makes me feel better to think anyone else kind of knows about it.
Tl;dr: the supposedly monster child of the family was by far the most abused and mistreated of us all and my parents were the bad guys.


Source.