Mate, I'll be serious for a second. I was in the same boat as you find yourself in, knocked about by a drunken stepdad and with a younger brother and sister to look out for, unfortunately in those circumstances the woman rarely takes action and I had to seek help from social services myself at the age of 14, it meant being placed in a children's home for a while but eventually it got resolved and indirectly got my mum the help she wouldn't ask for herself. She'll not take any pleasure from him treating you the way he does but I can almost guarantee there's very little she'll do about it, unless maybe he seriously injures one of you, at which point it's a bit late.
Don't kid yourself that he'll change, men like him just don't unfortunately and if things are as serious as they appear then you really need to get some outside help, otherwise younger siblings are gonna go through the same.
Anyway, I'm glad to have shared with the group today.