Ray & I did Natucket a year or so ago. We took the ferry over from Hyannis. Once on Nantucket we rented Mopeds (I've never been on one before) and easily rode to all the lighthouses.
Sankaty Head was beautiful. For Great Point we signed up ahead of time for a "Nature" tour of the area. It was a little pricey but well worth it. They drove us out to the light in a pickup truck that had seats in the back. The guide stopped periodically to talk about the birds, grasses, etc. The best part of course, was the lighthouse. She let us spend about half an hour walking around taking pictures. We then climbed to the top. What a breathtaking view. I would recommend this to anyone.
Great Point Wildlife Tour