Welcome back, Monique! It sounds like you have just over 75 days left until you set sail! You must be so excited! I'm glad you are thinking ahead about your Port Adventures, because as you know, guests who have cruised with Disney before are part of the Castaway Club, and are able to book their Port Adventures 90 or more days in advance, so some adventures will already have bookings by the time you log in.
Some Port Adventures do fill up, so it is a good idea to book as soon as possible. If you are all on the same reservation or your reservations are linked, you can
log in to your reservation and book this adventure, selecting each guest who will take part. If you have separate reservations that are not linked, one person from each reservation will need to log in to choose their adventures. Just be ready to do this 75 days out so that you can choose the same time. Have your names and reservations numbers ready in order to log in.
I hope this helps, Monique! I'm taking my daughter to swim with the dolphins at Blue Lagoon for the first time during our cruise in just a few weeks and can't wait to experience this adventure. I've heard it really is a great one, and I hope you are all able to experience it as well!
Let me know if I can help with anything else before you set sail!