Jeanie, it all depends on how many people are willing to sleep in the same room, and if they all have to be same sex (except for your husband and yourself).
Sometimes, suites on ships are bigger than standard rooms, but still hold a maximum of 3, 4 or 5 people, depending on the ship. There are family suites on the newer ships than have 2 bedrooms plus a pull-out sofa in the living room, which may or may not be less expensive than getting 3 doubles (you and your husband, your motherin-law and sister, your father and youngest teen) and 1 triple (your 3 other teens). Of course, I don't know the gender of your children so there could be some switching as needed.
Don't forget, paying more money for more rooms does have a positive side. You get more bathrooms (you know what it's like for 4 teens to need the bathroom at the same time to get ready for dinner!). You get more storage space per person and everyone has a bit more privacy.
Once you have chosen the itinerary and cruise line that's right for you and your family, you and your travel agent can figure out that best configuration for your family.