We stayed at YC many years ago and had a daybed, which my son slept on. He was small at the time, but I seem to remember it being a good sized bed. We struggle with the kids not wanting to share a bed as well. On our most recent trip, we stayed at the Wyndham in Disney Springs and were able to get a rollaway.
However, we almost always travel with an air mattress in our suitcase, because I never count on being able to get the rollaway or room type that we booked with the extra bed. They do make very portable ones that you can easily travel with, even in a carryon bag. If they complain about it not being as comfortable, a compromise is to make them switch who get the "real" bed each night.
There are some DVC options as well that may have a sleeper sofa of some type - you could look into renting points for one of those. We've done that a couple of times and it works out really well. Another option, which may end up being better as they are older anyway, is just to pick a cheaper hotel and get two rooms. That way you have two bathrooms as well, and everyone has a little more space. We did this recently for a non-Disney trip, and I have to admit, I got a little spoiled!