Welcome aboard, Jennifer! My family has been to Nassau with Disney Cruise Line many times, and we've enjoyed all sorts of fantastic Port Adventures. Your family will love visiting the Atlantis Resort. It really is one-of-a-kind!
Since your family wants to see Atlantis, but has different ideas of what to see and do there, it's really no problem because there are two perfect Port Adventures that you can enjoy, partly together.
I'd suggest that your family with four adults and three children book the
Atlantis Aquaventure trip. The three seniors can then book the
Atlantis Beach Day Adventure. You'll receive tickets in your stateroom letting you know where to meet up on the ship for departure for those adventures. I cannot guarantee it, but usually all of the Atlantis adventures meet around the same time in the same spot. If not, no worries. Simply meet your group, head to Atlantis and then plan a time to meet up with the rest of your party there. The Aquaventure folks won't get to go to the Atlantis Beach, and the Beach folks won't get to go to Aquaventure, however all of you are able to explore the rest of the shopping and lobbies at Atlantis, including the self-guided tour of the "ruins" of the ancient city and the aquarium. So, depending on what time both of your adventures set out, you might plan to meet right away at the entrance to the "ruins" to explore that together before heading to your own adventures in Atlantis.
Then, on the way back, there are multiple return times. Decide ahead of time when you want to meet up to return (or just return on your own if you can't decide together). You'll head to a designated spot to meet the motorcoach for return to the ship together. Have fun on your cruise!