Greetings, Bethany!
What a fun trip it sounds like you are planning with your brother and his children. Thank you for visiting the Disney Parks Moms Panel to ask us your Walt Disney World Resort planning question.
I wish I was better able to help you, but I ran into this same problem a couple of years ago when we were traveling with family. I needed access to my niece's
My Disney Experience account so I could plan her trip details with ours and her existing account was under my brother's. While it is a pretty easy fix, unfortunately, the only way I've found to get it changed was to
call the My Disney Experience Help Desk so that they were able to pull up the accounts and help me out directly on their end. They were able to make a couple of changes and I was able to begin planning our trip shortly after with ease.
Happy planning, Bethany, and if there is anything else we are able to assist you with, please let us know.
Magical Wishes,
Lauren