If you are coming back from a cruise, then maybe it would be better to rent a cheapie room by the airport so you can nap and shower before your flight.
In the good old days, most hotels had day rooms available for a nominal fee. I guess the cost of cleaning them sort of made that perk go away.
What replaces it nowadays seems to be the use of the hotels spa/pool facilities with lockers, shower, towels, changing room etc. I've often done this when I 've had a late flight and if I've stayed at the hotel the night before, it has always been comped. As I understand it...you will be cruising the night before, right? And you wanted to drive back to DisneyWorld for a last day at Disney before your flight? Why not have that day and then use the shower facilities at the hotel spa/exercise room. Maybe you could book a massage for you and they would let your family use the showers too?