I'm a little more experienced than you, but not much...and there are others who are far more qualified to add their thoughts... but I'll give it my thoughts anyway.
Other than the altitude factor, I think you and I are in a similar situation as far as nectar flows and hence, swarms. I think that the most important factor, especially for the first two hives you described is to make sure they have enough stores to get to the nectar flow. At this point, I would think that they need to have 4 or 5 frames of honey left. If they don't you're probably going to have to supplement them.
You have to start thinking about avoiding conditions for swarming. Are they bringing in any pollen? If so, the queens are probably laying well, and, you need to keep on top of the amount of room the queen has to lay. This would be especially important for the colony that hasn't gone into the upper deep yet. If the queen has run out of room to lay and she's surrounded by honey, you may lose a swarm (I think it's still a bit early for that in NW PA, but something to stay on top of anyway). If you have some drawn comb, consider adding a frame into the brood area to provide the queen more room to lay. If no drawn comb, perhaps you can exchange some of the empties from the two hives for frames of surplus honey from the other. If you do that, make sure you shake/brush all the bees off any frames before you transfer.
I hope this helps and would like to hear updates from you as I have a colony that is in a similar condition as your third one. It would be good to compare notes.