Breezy,
I have two grown children a well, and I know that there is often awkwardness as sometimes they are not sure how to respond or comment, or even talk about the RSD. They are loving and sensitive and I have always been a strong influence in their lives.
I think it's just hard for them to absorb that I have RSD and will not be able to do the things we used to share, (outdoor stuff, hike, etc)

Some friends no longer call because they just don't know what to say..It's almost as though I am a different person to them now...and in some ways I am..
I can't share many of the things we used to do together, along with the spontaneity.

I bring this up as it might be that your sons simply don't know how to put into words how they feel, and therefore don't communicate at all...
Would it help if you wrote them a letter explaining how you feel.....
Take good care,
Hope4thebest xo