I have not visited any of the ports that you list, but I can assure you that at the very least there is shopping and bus tours of the cities in Grand Turk and Freeport. Check the excursions list for your cruise and there will be a wheelchair icon on some of the excursions showing that they are wheelchair accessible. You may also want to email carnival here specialneeds@carnival.com and ask about activities.
Past/Future Cruises-
RCCL Sovereign of the Seas 4-day Bahamas 7/03
Disney Wonder 3-day Bahamas 8/08
RCCL Monarch of the Seas 4-day Bahamas 1/09
CCL Holiday 4-day Key West 5/09
CCL Legend 7-day Western Caribbean 9/09
RCCL Grandeur of the Seas 5-day Western Caribbean 1/10
RCCL Monarch of the Seas 4-day Bahamas 4/10