Please check with the Travel Agent or Cruise Line. Also most ports have a fleet of taxis and mini buses at the dockside looking to do business for the day and may have the correct vehiclesto accomodate all customer requests, also at competitive prices. Dont be afraid to ask and barter for the best deal. Have a wonderful crusie.
Why not call RCI UK and speak to their shore excursion dept and they will be able to advise what will be suitable. Alternatively if you look at the excursions for your cruise on the RCI website it will say what level of difficulty each one is.