3 separate bedrooms? I know it is common to have a "master bedroom" and then a "bunkroom" with 2-4 beds in it, but I don't think I've seen a 3 bedroom camper. For weekend camping it is common to drop the dinette table down to make an extra bed, but I don't think you want to do that for full timing.
I have seen some floor plans with a large bunk room in the back with doors on each side. They are really rate and definitely not current designs, so your going to have to do some serious internet time to find something that might work.
Just spent three day, 10 hours each day, at the LA RV show. The closest I saw to what you want is a 40 foot fifth wheel with a center room and a loft above that room. One model with a room and loft is a Grand Design Reflection 367BHS, there are other brands like that one by other manufactures.