Genuinely need some help

I am a 19 y/o female. My younger brother is 16. But the thing is he has gone astray. He physically, verbally abuses us. He has also been constantly failing his exams and he doesn't want to continue his studies. And the physical abuse has been getting too much lately. And honestly at this point there's nothing we think we can do to "fix him". And I honestly cannot do this anymore. Even if I try to fight back it just doesn't work. I know I sound pathetic. But I genuinely don't know what to do. My mother doesn't want to take any legal help. She doesn't want anyone to know. And my father has passed away recently.

So I am genuinely asking for some help. Is there any rehab/therapist/consultant that can help us? Or what should we do?