I was recently contacted by an organization that may be helpful to you. The Sibling Project was founded to provide peer support for siblings of kids with special needs. I'm sure you will be able to speak with siblings who will be happy to answer your questions and provide you with valuable insight.
Here's the link to my article on the subject.The Sibling Support Project
The Sibling Support Project was founded on the belief that "disabilities, illness, and mental health issues affect the lives of all family members." Find out how the project can help families in your community.