So annoyed with my sister

We're three siblings. I'm 16, Dave is 15 and Mae is 13. My whole life dad has been abusive and mom knows this and I've begged her to leave him because he's an alcoholic and he hurts us but she refuses to because she thinks she wouldn't make it financially without him even though I've said me and Dave will help pay the bills by working after school (we've got good grades and no problem with school) but no. Dad is verbally abusive towards all of us, he'll call us names and tell us how worthless we are and all that. But he's only physical towards me and Dave. He gets mad at Dave because he's "not a man". He's sensitive and shy and for that dad beats him. I love my baby brother more than anything (he's my baby brother even though it's just a year between us. We're very close) so I obviously can't stand it and anytime I see dad beat him up I interfere so then dad gets mad at me and hit me instead. I rather have him beat me up than hurt Dave honestly. So here's what makes me so mad. A while ago Dave ended school a bit earlier than I did and didn't wait for me like he usually does and went home alone. When I came home my dad had beaten him so badly he was unconscious and I thought he was dead! I yelled at dad and was so fucking angry and scared and picked Dave up and rushed to our neighbours and we went to the hospital and contacted the police. Dave is going to be okay but God knows what would have happened if I didn't come home when I did. Here's what makes me annoyed. Mae is writing all over social media what a horrible life she has and how dad is only abusive towards her! After our broder has almost been beaten to death! I can't believe her! I'm so pissed off. I confronted her at school and she didn't even seem to care. She just wants everything to be about her and wants attention and want people to feel sorry for her. I'm working after school at a cafe and Dave is there with me when I work. I'll never let him out of my sight again and I'll save my pay checks and the moment Dave turns 18 I'll get our own place and make sure he'll get into college. He deserves it. Right now dad is awaiting trial, mom still haven't divorced him and Mae lives with her but me and Dave are still at our neighbours (they offered us to be there). We have no other family and we refuse to be with our mom now.