In alot of cases, you can’t immediately solve the problem, you have to be patient while you try to navigate out of the problem. You’re in such a situation, I’m sorry, realistic ALL you don’t have an out right away.
But, convince your mom to get a divorce and claim alimony and child support, you should store as much proof as you can, proof of abuse, violence even his salary slips, You need to consult a lawyer and eventually go ahead with it. All the best. I know its easy to give advice, but if you choose to go ahead with it, it is going to be a bumpy road ahead. All the best