Why only one bed in a fifth wheel and why sooo tall?

Our fifth wheel has one queen, a couch that makes into a twin bed, and our dining room seats can be made into a full size bed when the table top is used as base. The queen is for the two of us and the other two are used for grandkids. We also carry a twin size air bed for if/when we are crazy enough to bring more than 2 grandkids at the same time. We have been on the road for 7 weeks but last we checked there are 7 of them! :-)