Let's see, what do I remember:

Really the only "requirement" for family time was dinner every night. Someone made sure we had two large tables close to each other that fit everyone - had to talk to the cruise line about that, and we just ad hoc sat down in a different spot at those two tables every night. Having that expectation - and no expectations about any other time - helped in avoiding hurt feelings that someone wasn't coming to something because they wanted to go somewhere else.

Communication is kinda hard without cell phones - if your cabins are in the same area of the boat, you could put up a dry erase board or something on one of the doors to send each other messages. We did know everyone's room # so you could call that way. Cruise lines have wi-fi and messaging available for a fee now. After a day or so we figured out where people liked to hang out, so if we wanted to see someone we had an idea what part of the boat they would be on.

Only a few people did excursions, they talked and planned them before. Through talking pretty much everyone knew what they were doing and where they were going and could tag along if they liked to.

The hardest thing for us was finding a place with a big enough table we could play games and things with everyone, where it was quiet enough. I think you can reserve specific rooms but I don't know how much that costs.

Have fun! People will joke about not going on cruises but there's a lot of pros about them especially for multigenerational travel. Not having to stress about food choice, preparation, cost, and cleanup is really nice and allows you to focus more on spending time together.