Beautiful, but terribly sad story, Cathy. I have no idea what the answer is, because disability changed the equation for everyone in the family.
I live in Australia, and was a teacher, and there are certainly worthy changes going on for the disabled to an extent. Still, when the child goes home at night, the problem is well and truly the family's.
I want to say your daughter is quite inspirational. She will meet and marry a special person who is willing to shoulder and include your son. Right now she is still young.
Thank you for sharing. :)