Until recently my DD11 has been using the air mattress I have brought each year (at POP mostly). This year my DM said she could sleep with her, she wouldn't mind. Aren't grandmas nice?
Anyway when we did bring the bed down I put it in my checked luggage and it didn't take up too too much room. I have twin size from Target. I think it only weighs about 3-4lbs. Also packed the small pump as well. If I was flying on an airline that didn't allow any free luggage (I know fly SW exclusively thanks to the no fees for 2 pieces per person, used to fly Delta) then I would pack it in a carry on. With 4 people you should be allowed 4 personal carry ons ( like purses, laptop bags, etc.) as well as 4 additional carryons. An airbed will fit in a carry on sized piece of luggage.
No flames here. You're not trying to cheat the system since you only have 4 in a room and since POP doesn't have roll aways the airbed is a great solution.
Before we had the airbed what we did with DD (when she was smaller she was a bed hog and would move around way too much for either of us (DM, DGM) to sleep with) was we would make her her own bed on the floor, between the 2 beds. We would get extra sheets and blankets and make her a nice pad on the floor. Using the bedspread folded makes a nice soft mattress.She also had her own blankie. It worked out well since she could use the shelf under the nightstand for her stuffed animals, LPS, and books. In fact, when we bring the airbed we still jam it in between the 2 beds. Just have to make sure I don't get out on that side of the bed at night.

Also, she likes being as close to us as she can get.
It think I only paid $10 for the airbed and $5 or $10 for the pump at Target many years back. A great purchase.
