Family advice

I honestly don’t know what to do or how to feel at this point... So long story short back in October my sister asked if I could watch my neice for the day because she was sick and neither my sister or her boyfriend could afford to miss work of course I said yes! I spent the day with her🥰 even took her to see my mother (in the nursing home at the time) and her great grandmother (lives on the other side of town) end of the day wanted to be nice and pick my sister up from work and drive her home so she didn’t have to catch the bus. We get to get house and her boyfriend arrived at the same time (he drives himself to work while my sister catches the bus every day) last time I saw him he was cussing my sister out for asking him to help her get the car seat out of his car to put in mine so I could take my sister and the baby to the nursing home to see my mother since he makes an excuse to why he can’t take them when she ask him. I confronted him about it and he started to get disrespectful to me words got exchanged and next thing I know I’m in a FIST FIGHT WITH HIM! He punches my glasses off my face! At this point I’m throwing punches half blind my sister holding the baby yelling stop the only thing I see out the corner of my eye as I’m fighting for my life at this point in my beautiful niece all sick watching the whole thing as I’m ready to throw another punch back at him my sister jumps in the way while holding her! I immediately stop! Run to my car call my fiancé ( truck driver over the road) then call my father! My father calls the police I bring my father back to my sisters house and her boyfriend no longer there (he ran) I give the police my info now it’s been only one court date. My sisters still with him. I tell my whole family how I feel about the situation and tell them he need to be in jail for what he did to me my mother says “you can’t take her father away” ( talking about my niece) and my mother still goes over to my sisters house and just acts like nothing happen BUT the most hurtful thing of it all is when my grandma says “I think your just jealous of your sister because she had a baby before you” OUCH! Because my grandma knows how difficult it’s been for me and my journey ttc. My father doesn’t like to talk about the situation at all. And my fiancé is eagerly awaiting his time to meet up with my sisters boyfriend. At this point I don’t know what to do I block my sister from all forms of contact she says we are both wrong but lately she’s been only on her boyfriend side since our first court date and they are saying I was “withholding the baby from him”.... would I be wrong if I moved back out of my parents house and stay away from my family! As in change my number go on the road with my fiancé and never look back?? I’m just so hurt and lost and depressed don’t know what to do