I mean your brother is right about the "your behavior is just gonna make it worse" part, it depends on how you live it. You see, if you don't talk because you're too scared of other people judging you then you'll always live in fear, but instead you can do some efforts to try to talk more and be at least a little more confident. I believe he doesn't know how stuttering works so he thinks that if a person can cure himself everybody can but this is not the case