I was in a similar situation in high school after my father died. My mother simply couldn't control my brother. They would get in physical fights. My brother was labeled a sociopath by psych workers for awhile. I had to clean up after him and do all the chores and he was really mean to me. Eventually I had to move out because he wanted to kill me. I hope you can move out soon, because that's likely the best way to get out of the situation. I would also just stay in my room and try to avoid him.