Your question is a bit of a thread hi-jack, but, since you asked...
You already answered your own question about having 2 hides in the 15 qt tubs, but I would offer at least one. The young BPs you'll keep in the smaller tubs will appreciate the security of having a hide.
Go with two hides in the 32 qt tubs. No reason not to. If your snakes don't use them, you can always take them out later.