Managing personal Outlook.com account settings, security, and privacy
Hi,
Let me explain in a simple way.
Microsoft 365 Family cannot replace your two Microsoft 365 Business Basic licences if you need two separate mailboxes/users.
Microsoft 365 Personal/Family provides Outlook.com email for personal Microsoft accounts. Family allows you to share the subscription with up to five other people, and each person gets their own Microsoft account and their own OneDrive/Office entitlement. It does not provide Exchange Online mailboxes for a business domain.
You can create multiple Outlook.com aliases on a personal Microsoft account, but aliases all belong to the same mailbox/inbox and account. They are not two independent email users/mailboxes.
I hope this information helps. If you have any more questions, don't hesitate to reach out.