Hi Katie,
Welcome to the Disney Parks Moms Panel and thank you for your question!
We often travel with friends and family members and it’s happened a couple of times that some people were either no longer able to join us for our trip to Walt Disney World Resort or they were only able to confirm their presence at the last minute. The ability to make any adjustments to your party size is at the discretion of the restaurant’s manager when you check in. I’ve only ever had a problem once where we weren't able to be accommodated at all (understandably, at the super popular
Be Our Guest Restaurant) and a couple of occasions where we had to wait an unusually long time for a table due to the change in our party size.
My suggestion to you would be to keep trying to
make a dining reservation that can fully accommodate everyone in your party OR to try to make a reservation for an additional party of 2 near close to your current reservation time. I've had much better luck "combining" reservations than adding people on at the last minute. If, however, you can’t make alternate plans, show up at your reservation time and explain the situation to the restaurant’s manager. Hopefully, they’ll be able to accommodate you!!
I hope my answer helps you plan your upcoming vacation and please don’t hesitate to come back and visit us if you have any other questions.
Have a Magical Day,
Lynne