NO MORE!

Me and my sister use to be best friends. She married a man that was convicted of murder. A 54 year old man just cashed his check and he gave him a ride home . He then took him out the car and kicked him to death. 15 years later they are married and now have a one and five year old. Three years ago I went to a party and seen him grab a 16 year old butt. I told him I was telling my sister. He made it outside before me and as soon as I open the door and stepped out he punched me repeatly like 30 times. Someone called for a ambulance . He got away with it. Two weeks ago he invited me and my boyfriend over after staying away from him for 5 years. He kept giving us alcohol . My boyfriend couldn't even raise his head he was so messed up. I tried to pick him up and here comes the brother in law . He starts to kick my boyfriend so I dove on top of him to protect him and took all the punches . My sister doesn't even care. It makes me sick because my mom doesn't want me to date a abusive man and just last week invited them both over for dinner. She's seen my head and face at work and never failed to even ask if I was OK. What should I do about my mom and sister?