how can I combine my two Microsoft accounts each with individual email addresses into one account?

You cannot merge or combine two separate Microsoft accounts. Microsoft treats each email address and its associated data, purchases, and subscriptions as independent accounts. There is no supported way to transfer a subscription, OneDrive data, purchase history, or other account information directly from one Microsoft account into another.

What you can to is to choose one account as your primary account. Since your Family subscription can be shared, if you want to consolidate around that account, keep the Microsoft account that has the Microsoft 365 Family subscription and consider canceling the Essentials subscription on the other account so you are not paying for two subscriptions.

You can then share the Family subscription with the other email address. This does not merge the accounts, but it allows the second account to receive the Microsoft 365 benefits under the Family subscription. The two accounts will still remain separate.

For email, you can add both Microsoft accounts to Outlook and manage both mailboxes from the same Outlook application. This gives you a single place to work with both email addresses without actually combining the Microsoft accounts.

For OneDrive files, there is also no direct account merge. You can manually move the files from the OneDrive associated with the account you intend to stop using into the OneDrive associated with your primary Family account. Before canceling anything, make sure the files have been copied successfully and that you have access to everything you need.

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hth

Marcin