In Roatan you will have to get a taxi to get to the beaches, they are a good distance away. But the goods news is that there are taxis to be had OR you can find a tour guide that will drive you whereever you wish to go for a price. You can find a van/bus that can handle 7 people I am sure. Do a web search on Roatan taxi/tours and you will find some options. For beach choices there are a few. There are also several resorts that you can get a day pass from. I have been to Foster's West Bay a couple of times. The offer a pay one price beah day (and optional snorkeling tours for an extra fee.) You can also get a transportation/beach package from their website. They answer emails.. write to them and ask about what they can offer. Or you can just show up in Roatan, go out of the port entrance and negotiate with a local tour guide to be your transportation for the day (this way you don't have to make a decision until you get there and see what the weather is like) You may get a better price this way, you may not. It depends on your bargaining skills. We got a all day tour taxi for $80 for a family of four. We might have gotten it for less but we thought that was a fair price. The bigger the group the less the per person charge is going to be.
Cozumel- The swim with the Dolphins excursions are popular (although expensive). Just be careful in making sure you book the tour you want, there is the Dolphin Encounter which is you see the dolphins and maybe throw them a fish or 2. Then there is the dolphin swim where you get in the water with them and they interact with you (pull you along.. play fetch etc...) There is a big price difference here also so make sure you know what you are getting. Personally, having been to Cozumel so many times, I don't book anything through the ship. I just walk out to the taxi area and arrange a tour there. There are many resort operators that will have vans waiting trying to get a group to go to their beach resort for a day and you can find goo deals for large groups. Don't be afraid to negotiate a good price.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14, Freedom x 2 6/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013