Welcome AlexSantos!
Sorry to hear about your parents, when he is sober you could say to him that violence is never acceptable and that you would report him if he became violent. You can also tell how disappointing his behaviour is.
That said if he is to change then it would have to come from within himself, it cannot be done solely to please others.
If you look on the list there is a forum headed "Friends and Families..." which you might find helpful as i'm sure there will be others there in a similar situation.