You could try putting down in your search 1 room, 5 adults. Most US hotels websites will let you put 4 adults in one regular room with 2 beds. But if you put down 5 people in 1 room, most likely you get nothing or room with 2 bedrooms. Many of the 2 bedrooms suites will have max occupancy of 5 or 6 adults as they will probably have a sofa bed in the living room.

However it seems like it is always cheaper to book 2 rooms.. a lot cheaper. And some hotel gives 2nd room 50% off if it is for the kids.