I had the same issue, and for me the cheapest was to get a connecting room cat 10. It was a few hundreds more for the cat 4 which is the lowest category you can all fit in one room.
Usually getting two connecting or close to each other staterooms is the least expensive way to go. To get everyone in one room will require a minimum of a cat 4. The other advantage to 2 rooms is two bath rooms & more space.
We are booked for two connecting cat 10 rooms. On our first cruise we had rooms side by side with Grandma. It will be nice to knock on Grandma's connecting door this time ('06) in our jammies than knocking on the outside stateroom door.
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