Find out from the ship the door width. Have not traveled on this ship. You also need to find out about the bathroom set up...most require a 4-6 inch step up to get in, and many have only tubs instead of showers.
If you are not already paid up and committed for this cruise you may want to look at other ships. There are many other ships that do have handicapped cabins that will take 3. We have had good success with HAL, Princess and Celebrity in this regard. Most often the 3rd bed is either a bunk, a sofabed or a roll-away. It is pretty cozy though!