Our wedding is in Jamaica, so I can't really help you with specific activites, but we are only planning one group activity. We will hopefully do a group trip to Dunn's River Falls. Of course, we will also have our wedding reception and a welcome dinner.
Last year we went on a cruise with about 10 people of all different ages. Nobody in the group ever chose the same excursions. It is very hard to find activities that everyone is interested in, especially when there are so many choices. I would suggest you and your FI choose what you want to do, then maybe just let everyone know what you are doing and that they are welcome to join you. That way people don't feel like they have to join you if they don't want to.
You could drive yourself crazy trying to please everyone, so just make sure you do what you want!