Does it matter which MDE account you link your tickets to? I have an old account that I’ve used for me, my ex and my kids in the past but I have a new MDE account that just has me on it Can I create their names on that account and link tickets to a new trip on that MDE account?
Do you have old Magic Bands? If so, you won’t be able to use those on the new account.
I would contact Disney IT via MDE chat and ask them to merge your accounts.