Welcome aboard, Mandi! I bet you are really looking forward to your Fantasy cruise this fall!
I'm happy to let you know that you and your husband are welcome to head off on your favorite Port Adventure while your parents take your little ones off on a Port Adventure more suited for them.
As long as the Port Adventure information does not specify a legal guardian is required (only a few do), your parents can easily take your kids on an adventure. Since you will not be accompanying them, however, you will need to stop by Guest Services once you are onboard to pick up a Parental Debarkation Authorization Form. This form will give your permission for your parents to take the children off the ship.
If your reservations are linked with your parents' reservations, you shouldn't have any problem booking your parents and children together on adventures online. If you do run into an issue where the computer system isn't allowing you to book them together, give Disney Cruise Line a call at 1-800-951-3532 and follow the prompts for the website assistance team. They can help assign those Port Adventures for you at that point.
So, find your perfect Port Adventure, and check out the
"Family Adventures" which will be wonderful for your parents and little ones, and get ready to set sail!
I hope that helps as you plan your exciting cruise, Mandi! I'm happy to help with any other questions you might have, so feel free to stop back here as you continue to plan!