Thanks for the replies thus-far.
The smallest is a compact stella cherry, which should be about 10-12' tall, according to the nursery. The others seem to be about 16-18' tall. I have no idea what that'll equate to width-wise. :?
We live in a suburban subdivision, so our backyard is roughly 60' wide from fence to fence. I was hoping to just evenly space them out across the far end of the backyard, but if I need to keep 10-15' between them, I'll only have room for 3 there (since I can't plant them on the edge of the fence, obviously).
I'm thinking maybe the stella cherry can go in the front yard. The front yard gets a lot more sun, though... much more than the backyard. They're both what I would call "full sun", but our home faces south so the front yard gets the extreme mid-day temps, which in TN is about 98-ish degrees.