To be honest, there's not a lot you can do. People who have an immature social level are just going to continue and pick on him because they feel it's the funny or cool thing to do. You can't expect tons from that age group, honestly I hope your brother can see that he shouldn't worry about what other people think about him, because in the end it's only going to matter what he wants to do for himself.
If he ever wants to change, he needs to do it for himself. Worrying about it on the other hand isn't going to help him, he shouldn't have to prove himself to anyone, it's likely that if they don't accept him for who he is, they don't need to be in his life in the first place.
In all honesty, I say you talk to him about this. Lend him this advice, tell him to keep his head up. If he goes through this a lot, and he comes out of it. It only makes him a stronger person, and it makes the other kids weaker people. Hopefully he never sinks down to their levels either. Eventually he'll find people who accept him for who he is, and he can be happy that he has friends, and I hope it works out for him that way.
If he ever wants to change, he needs to do it for himself. Worrying about it on the other hand isn't going to help him, he shouldn't have to prove himself to anyone, it's likely that if they don't accept him for who he is, they don't need to be in his life in the first place.
In all honesty, I say you talk to him about this. Lend him this advice, tell him to keep his head up. If he goes through this a lot, and he comes out of it. It only makes him a stronger person, and it makes the other kids weaker people. Hopefully he never sinks down to their levels either. Eventually he'll find people who accept him for who he is, and he can be happy that he has friends, and I hope it works out for him that way.