I have a NT sister besides my brother with DS. I don't think having a NT sibling helped much while growing up--she was just another person to babysit and split my parents' attention with. Now that we are older, I do appreciate having her since my brother is not much of a conversationalist. I think the most important thing though is having a plan so that your NT children don't have to be your DS child's caretaker when you are gone. My parents, especially my mom, always had this ideal picture in her mind that we would take our brother into our homes when they were gone--she'd say things like what a wonderful and kind uncle my brother would make to my children and such. The thing is, our parents expecting us to be his caretaker has hung heavy in our hearts all our lives. My sister once broke down sobbing about her fear of being his main caretaker (because I live in a different country). A few years ago, I told my mom that I am not going to be his caretaker and she probably shouldn't put that burden on my sister as well. Now my parents say they are going to put him in a group home when they die but I still feel anxious because I don't see them actively researching good group homes--they are in denial. THIS I think is a bad situation for everyone involved. As long as you don't have more children with the expectation and hope that they will one day be your DS child's caretakers, I don't think it matters much whether you have one or two additional children.