Hiya Kristen!
Welcome to planDisney! Visiting Walt Disney World Resort with even more friends and family sounds like so much fun! I love enjoying my favorite place with my favorite people. I once visited Walt Disney World with 12 other people and found the planning pushed me to learn as much as I can to make it magical for everyone. It was a little intense but I promise you that we here at planDisney are here to help you!
To make changes to an existing vacation package with Costco Travel it appears that you have to reach out directly to Costco Travel. Since they are essentially your travel agent they are the ones who will have to make any changes and do it in such a way as to avoid any mistakes.
Once you add your guest and get a Reservation number or Vacation Package number from Costco Travel, head
over here to link it to your
My Disney Experience account. You should see the people on your reservation under
"My Planning Party." If you don't see them all then that means you have to link them to your
"Family & Friends List" Just click on "Add a Guest" at the bottom and search for them or make an entry for them. I have made an entry for my kids and for my mother-in-law who don't have phones. Now I can plan for everyone by booking
Dining Reservations and
Enchanting Extras. Don't forget that you can start booking these things 60 days before you arrive!
I hope this helps and that you have a magical time. If you want any tips for large groups feel free to
reach out to me!Happy Planning!
-Nimmy