Wendy,
We did the exact same thing 2 years ago in 2 Cat. 10 rooms...me, my DH, and my 2year old DD in one room, my mother and 3 DS ages 3,5 and 9 in the other. It was fine, you don't spend a lot of time in the room anyway. It's worth getting the 10 rather than the 11/12, the split bath is very helpful when getting that many people ready for dinner!!!! In all, 7 people in the 2 cabins worked out just fine for us. I checked in to the family suites which sleep more, but not 7, and the price of moving up category wise with that many people is substantial. You will love it!! Have a great trip! We enjoyed it so much that my husband and I leave 3 weeks from Sunday ALONE for an anniversary cruise!!!
Chris