Royal CAribbean's Voyager Class ships have a number of family staterooms that fit five. You're smart to look into it early since those larger staterooms fill up early. Your teen will love Royal Caribbean's teen program. Royal Caribbean is one of the few cruise lines offering private babysitting for children six months and older, which you might want to take advantage of.
Feel free to ask any add'l questions. You may also want to read the article I've written on this site, "Bringing the Baby" which answers a lot of questions about cruising with kids.
Luisa Frey Gaynor
Family Cruise Editor