Maybe you should talk to him? If he lashes out then don't talk to him until he is calmer. Let him know how you feel or talk to your mum and sister about it.
I’m sorry to hear you have to deal with all that; you shouldn’t have to, especially when it affects your school life too. I really don’t know what advice to give you because I don’t know a lot about the situation, but if you ever need someone to talk to just send me a message because I know what its like having people think everything’s fine when all you want to do is scream and tell them its not, but then you cant because you don’t want them to know how it really is.