Stufus:
I'm sorry to hear that physical circumstances have altered your plans. What ever challange you & your family are facing, I hope you come throught it well & easily, or at the very least, this cruise helps you to cope.
I haven't been to all of the places you are going. Based upon your use of "physical" limitations, I am going to give you what answers I have based on the ASSUMPTION that there are mobility or stamina issues. My bias is based on the fact that those are the limits I deal with regularly w/ my family. Anyway, here goes:
San Jaun: This is an old metropolitan city & very HILLY. Walking it yourself is not a good idea. If you can do some walking you may want to take a taxi to Fort Morro & look at the view. If that's not an option, you can still get a pretty good look sailing in & out of the harbor on the ship. Since you have to make choices, I'd skip this port & view it from the ship. Especially if it is your departure point, you need to rest for the other parts of your travels.
St. Thomas: We went shopping in the city, Charolotte Amolie (I spelled that wrong). The shopping was phenomenal. If you are not into shopping, you can stay aboard. However, there is some shopping right at the dock in Havensight. It's flat & not very strenuous. It may be a way to pass a pleasant hour or two. There is a cable car "ride" up a big hill near the dock. You can take a cab. We walked; it's about a 5 minute walk at a moderate pace. The view from the ride & at the top is magnificent. Again this may be an easy / quick thing to do to get an overview & feel as though you've experienced the island w/o it being too taxing. There are junky souvenier shops up top & a bar if you are having a "good day".
St. Kitts: We took a lovely tour in a minivan w/ a woman named Mrs. Wallace. She only takes 6-10 people & the price per person varies by the # in your group. Anyway, she picked us up at the dock & took us all over the island in air conditioned comfort. You could see a lot just from the van. We walked through an uncrowded botanical garden (which she said gets crowded later) & then went to Brimstone Hill. This is an amazing fort built in the 1600's by the British & French. It was certainly not built to OSHA or ADA standards. While it is an architectural wonder, you may not enjoy trying to climb its uneven surfaces.
Barbados: Skip it. It's a very poor country & there will always be somebody trying to sell you something. The vendor will not take no for an answer well. The best things to do are beach excursions. So if you are trying to conserve your energy, hang out by the pool. It's the same sun after all.
St. Lucia: You MUST do the Pitons (not climb them but at least get to see them). Land & sea may be a bit overwhelming. It's an all day event but the land or sea only (your choice) will give you great views of these amazing twins. If you think you can make it, I was fascinated to go to the volcano. The "problem" is your phsyical limitations may hamper your enjoyment of this part. It was rocky, uneven & steep. It also smells like rotten eggs from the sulfer.
I have friends who love Aruba & say it's the most beautiful island in the Caribbean. I've always wanted to see the sideways trees & square coins. I understand the local vendors are very polite.
If you are feeling energetic with a bit of research before you sail, you should be able to find more non-strenuous excursions -- touring from a bus or some such activity-- that will will enable you to get out a bit without over exerting yourselves or your pocketbook.
Enjoy.
