Aww...i am glad to hear that things are going well.
I have six and they all use whichever box they please. Not all of mine have all of their claws and they are fine with regular litter, so your declawed cat may surprise you and use the regular litter. As long as both don't have any parasites, I don't see a problem with sharing boxes.
I have only tried one fountain and it got gross in a hurry. I just let them play in the bathroom sink when I am in there and leave out a bowl all the time.
Love the pic...such pretty kitties! :)