Try
cruisestateroom.com.
On the Millennium, we stayed in room 2016 - it was an ocean view, no balcony, but it had: two lower beds, two beds that dropped down from the ceiling, and a sofa-chair that converted into a twin - might have been cramped, but it could have slept 5 people.
So there are options. Check out the little symbols on the deck plans that mean "upper berths" and "sofa beds." Then you can be sure to book a room that will fit everyone.
Cheers,
Michelle B.