I don't understand the difficulty.
Most fifth wheel trailers, at least half of the travel trailer offerings, and most Class A motorhomes, especially the larger ones, are configured like this. If they sleep more than two people, it is by converting living area furniture to beds.
Class C motorhomes are the only type that typically have two sleeping areas, but the subset called B+ does not, and may not even have one dedicated bedroom.
Families seeking separate bedrooms or sleeping areas for children have more difficulty finding something suitable.
There are a few manufacturers, like New Horizons for towables, or Newell for motorhomes, who will build the layout of your design. In the first case, starting at about 30 feet, but at Newell, all the coaches are now 45 feet long.
