I've lived in several houses that had 2 bedrooms, a bathroom (with tub/shower), a kitchen, and laundry closet that were 8-900 sq ft, so to me it seems profoundl

I've lived in several houses that had 2 bedrooms, a bathroom (with tub/shower), a kitchen, and laundry closet that were 8-900 sq ft, so to me it seems profoundly unserious to suggest you can't fit a small adult only room (think more like a walk in closet) in that space. Ignoring that, they don't even need a room. They just can't let kids access it. A locked armoire near the checkout ought to suffice.