Trouble linking gamertag for a child account

Good Evening 

I see many people have posted about this but i believe, I might be unique.    I have my EA account (ON3J) and i had both my children as family on it both have aged out, however one of them linked their Xbox gamertag to the child account before the aging out, also he's somehow not showing in my family. I don't have actual access to that EA account, His old EA ID is [REMOVED] we aren't sure what email that separate/old account is on, but we do know the phone number and were able to reset that password.  Anyway, I could get that email address that my child's account was originally put on?  or is there any way to delete that old EA account and link his gamertag it to the new one [REMOVED]. We know a alot of the email address however it was quick email setup and forgot like 2 letters..HAHA   Tr*****@yahoo.com or you can delete that old EA account and link the Gamertag to the New account.  I really appreciate all your help please. 

Edit: Removed player IDs. Please do not post other IDs than your own on public forums. -CM