lifelong care?

I'm actually posting 2 days in a row, be sure you read the March 2nd post before this one.
The case workers for Kajon and Kajonae finally read our home study and both had the same immediate and strong response - they can't live with us. Their grandmother lives about 2 blocks away and there are some issues with her, so much so that it's important the kids don't live "around the corner." I guess I saw this coming (not the exact reason) so it's not as disappointing as it would've been if I hadn't already known there were so many people interested in them.
So here's my dilemma: there are some kids available that may need lifelong care, do we want to take that on? There are the 3 I mentioned a couple of posts ago, one with Down's Syndrome and there are 2 boys, also quite young with a list of both emotional and medical issues. One of the boys has microcephaly and Russell-Silver syndrome. I encourage you to look each of those up on your own. Microcephaly is characterized by a small head size, with it could come a wide array of complications, but think of the skull being smaller, therefore the brain being smaller and with a diminished capacity to function. Russell-Silver Syndrome is a form of dwarfish (their mother has dwarfism), though the most treatable. A good diet and growth hormones could put them back on track.
We expect whomever we adopt to have "issues," predominantly fetal alcohol, attachment disorder and often aggression. It is possible that they could be so extreme that they would not be able to live independently. Taking on a child that may need parenting beyond our lifespan is my biggest concern with taking on one of these kids. It's not the here and now, I think we can handle that, but what about as we age or upon our deaths? I guess that will be the reality for these kids no matter who adopts them...
Do any of you have any thoughts for me? Words of encouragement? A dose of reality?