<human>: Can you condense the text into a few key points?

My dad hurt my sister when she was younger... Around 13, possibly like 15? He'd get her stoned or drunk and molest her. I never asked and was never told exactly how, don't even want to know tbh. But I'm super protective of her bc I feel like her getting hurt is somehow my fault.
I am five years younger than her. My dad's off paper now, and out of prison but my sister isn't over it and honestly I don't blame her. He never did anything to me that I can recall but my sister wasn't blood related to him so that might be why, idk. But I do remember getting taken out of my home and forced to talk to a CPS worker, then on to living with family for a few weeks and the back with my mom. 
Flash forward to 12 years later, he's still my dad and I still hang out with him although I have a hard time looking him in the eyes or calling him dad or anything.
My older sister and my nephew need a place to stay until June  and I have a spare room but he won't stay away, no matter what.
I don't know what to do, I just want peace. I miss my sister and my little nephew but he won't stay away. He's just saying she needs to get over it, but my sister has PTSD and bipolar disorder and other mental disorders, that I'm unsure of and the last thing she needs is too be tormented by her abuser.

I was like literally thrown in the middle of this. My grandparents on my dad's side basically would drag me into a car for a super long car ride to visit my dad in prison, and my sister would (and family on my moms side) were always and still shit talking my father.

Apparently I'm still stuck in the middle... My sister asked if her and her baby could stay for a week and my father said "no one is going to stop me from coming over"

I don't want to drag cop drama into this, that's for sure.
I just got this apartment in January and I don't want any reason to be kicked out.
<bot>: My sister is just trying to escape her abusive boyfriend and needs a place to stay but my dad who molested her in the early 2000s won't stay away.