"your brothers brain works differently" maybe have a family movie night and watch mozart and the whale, rainman, temple grandin, or any other movie involving autistic main charectors.

Thanks for all the help. I feel ready when my other boys ask me.

My older two kids were 6 and 9 when my youngest was diagnosed. We got a bunch of books out of the library, but the one they liked best was "All Cats Have Asperger's Syndrome". Youngest DD's diagnosis is actually HFA, but I explained to them what the developmental pediatrician had said about HFA being like Asperger's but with a speech delay.

There are children's books about a sibling with autism. Ask a librarian.