this is something that your Travel agent is supposed to handle for you and should have already done so and gotten back to you with the infomation. Call your TA immediately and tell them your situation and make sure they notify RCI so they will be prepared and have you in a handicapped cabin! Very important!
Robo has it right, this is Travel Agent territory.
I looked at your itinerary. You should not have a problem in Nassau (I can't remember ever tendering at Nassau) but CoCo Cay could be another story. We have tendered at other private islands.
Just spending the day onboard is not a bad thing.
Robo is also right on the handicapped cabin. Gently insist that your cabin be on the boat (as in lifeboat) deck if at all possible. Your situation is unique.
If you have to "juice up" your wheelchairs with electricity, make sure that you take a heavy-duty power strip with you.
You may also want to check your dining seating assignment ASAP to make sure that you don't have to motor all the way across the dining room to get to your table. The dining room staff is very accomodating for such requests.
Bottom line, make SURE that your TA knows about your challenges and gets right on it.