It may just take some time.
As for the snapping - when is it happening? It could be communication and as long as Kasee is 'listening' then I would let the dogs work it out. You need to intervene if you see it escalate or one of the dogs isn't 'listening' to the other.
Not sure about the whining.. where do the dogs normally sleep? If Dexter isn't used to sleeping in the room, maybe try to let him have his own routine back?
I agree with lots and lots of exercise.. tired puppers make for good puppers!