Help with preserving a different MS account

Hello,

While my children were living with their mom, someone there had made my one son ANOTHER email address and Microsoft account. Mainly all of the purchases were made on said account. I now have custody of them and would like to take primary control of his XBox account so that we can make sure he does not lose any of his purchases when the sign in abilities for the Gmail account tagged to his MS account is no longer accessible.

So, I have a Gmail account that I made for him when he was born and a less frequently used Microsoft account is tied to said e-mail. How can I assign THAT email to this other Microsoft account? If I go to the one that was made at his moms house and try to add the email I made for him, it wont let me as it say's this email is already in use. How the heck can I straighten this out? I don't really care if I lose all of the purchases I made for him on the OG account.

To clarify things a bit and so we can break this out into a step by step a little clearer, the account I made for him is G********* Die E-Mail-Adresse wurde aus Datenschutzgründen entfernt. ***

The one I'm afraid we are going to lose access to is B************ Die E-Mail-Adresse wurde aus Datenschutzgründen entfernt. ***

Thanks!

Mike

:)