Wow! I think it is good that you are moving. It is an indication to you and them that you are recognize that their "status" has changed and your role has changed. Life moves on and you are ready,willing and able to move along with it. They too will need to do that. You might, since they have some special needs, make certain allowances for a limited period of time. I'm talking a year or two. So, perhaps help out a little more than perhaps typical for the next year or two with advice, financial matters, etc. But, that is about it. Our involvement grew less and less and then at 21 it was greatly reduced. Basically, our difficult child adopted child moved out at 19 and we slowly weaned her of our help. Today, in her early 20s, she knows not to count on us and is largely independent. There are times it is frightening, as she does not always make good decisions. Our involvement now is very limited. She has improved ever so slightly...but I do not concern myself particularly. Detachment is key.
I'm so happy that you have family to be with, that they have adult mental health counselors and that you are embracing this opportunity....Blessings.