Keep in mind that it is a short vacation, and having Grandpa in with the kids or even with you two might be fun. The bonding that occurs or a cruise is incredible! I just took a 7 day with four kids in a room, FYI. I also took a 5 day with my mother last April. A large part of the fun comes from goofing around behind closed doors.
If I were you I would pick and outside for you and an inside for the three of them. No question. Forget the suite- you will pay three times the price.