I have stayed at Caneel Bay and also at Gallows Point.
I liked them both a lot and would return to either in a heartbeat.
Gallows Point is close, walking distance close, to Cruz Bay. There are a fair amount of steps there as it is built on a hillside. Also, the walk to town involves a decent size hill. If they are not very mobile it might not be a good choice.
Caneel Bay is fairly flat and has very few steps. There is not much to do there other than relax and chill, and that's enough for many.
I believe that Caneel Bay, in keeping with their relaxation policy, does not have TV's in their rooms (you may want to check on this). Not sure if they have wifi either. They do have several of the most beautiful beaches in the VI's. Finally, Caneel Bay has a great restaurant onsite, Zozo's. Even if you're not staying there it's worth the trip.
I've never been on the Westin property but have seen it from the road as well as from the water. Looks very nice.
Good luck, the Virgin Islands, and St. John in particular, are fantastic.