I was an only child, but my two kids get along pretty good. They're 13 & 11 now. They do "bicker" from time to time but never do anything like you say your brother does.

Now, when you say your parents say "nothing we can do..." that is the source of the issue. He got this way by his (your) parents not working with him when he first started doing it. Definitely not your fault - he has anger issues, needs parental help and also probably professional help. Knowing this, you can start to either be part of the help (give him empathy, love and some boundry rules he has to respect). Parents also have to use boundaries and parenting to help him through this. Like any disorder, it can be helped but only if he finds that he is the source of the problem and is willing to help "you guys" help him.