I'm going to tell my brother not to listen to dating advice from girls
Why do you think he needs advice?
I've seen two of his exes, and they were both crazy
It is hard when you see your siblings making mistakes and it is okay to want to protect them. It will help them lead better lives.
It would suck for him to get married to a crazy girl.
That why you are there to help him make wiser choices. You should make sure he knows you have his back.