Abusive Brother

from the start, my brother has been extremely abusive. Mainly verbally. He yells at mom and calls her a "midget bitch" and he'll say things like "your hair looks shitty like that" or "you've gained weight fat bitch." to my mother. I try so hard to build my moms self confidence back up but my brother is fucking crazy. I don't know what to do at this point. If anyone has any ideas on how I can handle this, PLEASE let me know. I'm done seeing my mother upset.