Here's another idea. Or, parts of other ideas in a new way. I think. It's still early here...
Anyway, put your two twins fore-and-aft long the sides, but near the forward bulkhead of the bedroom, instead of aft, so you can use squared-off mattressses. But, instead of having a nightstand sticking up between them, make the nightstand low enough you could put a piece of plywood over it without touching. Then cut two pieces of plywood the size of the mattresses, and put the plywood under them on the bedframes. Then, when your yougsters show up, lift off the mattresses, turn the plywood sideways, and shove the mattresses together, making a single queen bed.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.