Royal Caribbean has Royal Family Suites that sleep 8 - one "master" bedroom that sleeps two, a second bedroom with two lowers and two bunks and a pull-out sofa in the living room. It has two bathrooms as well. Not sure of the price - depends on ship/itinerary, etc. - you'd have to call as these are not listed on their website.
A less expensive alternative would be getting two connecting cabins, one that sleeps four and one that sleeps three. It would be like having connecting hotel rooms - you can leave the door open in between. This would also give you two bathrooms.