Sting Ray City, Botanical Gardens, and Turtle Farm in G.C. Dunns RIver Falls in Ocho, although it's insanely crowded.

gc - taxi to rum point then use red sail sports to go to stringray city on their glass bottom boat. (i'd make a reservation) http://www.redsailcayman.com/redsailcaymanactivityrum-point
your parents can hang out at rum point while you go out, although it's not strenuous, assuming they can get in/out of the boat. botanical garden is lovely & en route from ship to rum point.
http://www.eandbcaymans.com/2Attractions%20a%20Rum%20Point.htm
http://www.botanic-park.ky/

at ocho besides dunns's you could go to http://www.rainforestadventure.com/jamaica_ocho_rios_tours_excursions/ has bobsled ride, zipline & chairlift ride through the trees, pool w/slide, butterflies & humingbirds.
rafting on the martha brae is fun (40 mile drive from ocho) http://www.jamaicarafting.com/
options to dunn's are mayfield falls or YS falls -both further (but more laid back) than dunn's so could use up the whole 7 hrs.

I agree with the recommendations for Grand Cayman. Grand Cayman is definatly the place for snorkeling. Pick a company that does the 3 snorkel stops and then Sting Ray City.

In Ocho Rios, avoid Dunn's River Falls. It's too crowd and full of aggressive vendors. Lots of walking and the falls are little too rapid and steep to actually climb them unless you are in very good shape.

Instead take a tour to Shaw Park Gardens and Coyabo Gardens. They are right next to each others and both have lovely foliage and waterfalls. There is a lot of walking so wear good comfortable shoes.

Rafting down the Martha Brae was fun also, but we enjoyed the gardens more.

You do need to take some kind of tour in Ochio Rios. If you don't want to use the ship's tour than book with a private vendor. We used A-Z Jamaica Planners. Ocho Rios is not a port you want to just walk off the ship and take your chances with the vendors at the end of the pier.

If your interested we have pics of the falls and gardens here:

http://travel.webshots.com/album/581974779NFDluV?start=144

I appreciate everyones commens and suggestions thus far - this has been a huge help.I was leaning towards snorkeling in G.C. and now that is a definite. KVR when you say pick a company taht does the 3 snorkel stops, do you mean you snorkel at 3 seperate places? Hope that is not a foolish question - and can you snorkel at Stingary City? Thanks!!!

When we went many years ago we used Soto and we did 3 snorkel stops and then went to Sting Ray City. You don't snorkel at Sting Ray City. It's sand bar that you can stand on and the rays swim around you. The guides give you squid to feed them and they take pictures.

Many people coming in from cruise ships use Captain Marvin.

Here are our pics from Sting Ray City:

http://travel.webshots.com/album/99827183ctjVpQ?start=36

We went before I bought a water proof digital camera. We bought the DVD of our trip for $60. It is awesome.

You might check the cruise critic ports of call forum for recommendations of operators.

www.cruisecritic.com

I've been on a couple different charters out to StingRay City. I used Sotos, and thought they were great because they take smaller groups. However I don't remember (3) stops AND Stingray City....it was 2 snorkel stops, and then Sting Ray City. Prices were very reasonable. The two things you want to avoid are booking through the ship where you will pay a lot more than booking on your own. And 2nd, make sure you book a smaller charter. The large boats are known as "cattle boats", and it's just as good of an experience as with the smaller parties. My guess is that a place like Sotos or others will send a van to come get you off the docks....

We went in 2003, so things might have change a little since then. We did do 3 snorkels stops and then Sting Ray City. We had a small group of people also. The smaller the better.

Is Grand Cayman still a tender port? We went back in 2007 and it was. If it still is, make sure you give yourself enough time to get off the ship to your excursion if you book with an independant operator. It can be very time consuming getting off the ship.

Thanks to everyone! I booked the stingray city and snorkel through Sotos, very reasonable I thought ($35 pp). Looking into Mystic Mountain in Ochos Rios, just unsure of what I want to do exactly. Thanks again!! Any thoughts on 7 mile beach? Sotos says they will drop us off there before we head back to the ship -and then we can walk to ship, they said about 15 min. or take a bus. Is it worth snorkeling/seeing this beach? I will have all afternoon open - about 3 hours or so. Thanks again!