In Old San Juan, there is also the free Trolley that you can get on and off at many historic sites. Take it to the top of the hill to El Morro, then the walk down will be a lot easier on everyone or just hop back on and get off where it is interesting to you. In St. Thomas, take a taxi to Maegen's Bay for some great beach time in the morning, then return to the ship in the afternoon for lunch. You could also take the Paradise Tram up the mountain right across from the Havensight port. For shopping, either plan on downtown Charlotte Amalie or right at Havensight Mall.
Bon Voyage