Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello, glad to assist you today.
You can sign in to https://account.microsoft.com/services using the account that owns the subscription. Click Share Microsoft 365 and check if his email shows as Pending. If yes, resend the invite and ask him to check Spam or Junk. He must accept the invite while signed in with the same email address where you sent it.
After he accepts, he needs to sign in at the same Services page and click Install on his device. You do not need to delete any email account. You only need to make sure he signs in to Office using the account that accepted the Family share.
Hope it helps, please let me know if you have further questions! Cheers!