What should i do? is this wrong?

Well, as you said, they're going to do what they're going to do. It's wrong that your brother was jumped and it's wrong for them to retaliate with violence because it will, most likely, just perpetuate a circle of violence. Still, as you said, they're going to do what they're going to do what they're going to do. All you can do is share your thoughts with them and stay away.