Joe - I don't know how you are going to "squeeze in" with your family in a 3 person cabin. There will be 2 twin beds and one sofa bed that sleeps one person. That's a pretty tight squeeze, unless you and your wife are used to sleeping on a twin bed.
Guess it could be done.
Have you called HAL Reservations or your TA to see if possibly one of the 4 person cabins is booked by only two or three paxs and therefore you could switch with them? It's worth a try. I'd get on the phone tomorrow and check this out.