How to upgrade from Microsoft 365 Personal to Family with Apple.

The current Microsoft 365 applications have an in-App family purchase for $9.99 USD. That would be a monthly charge upgrade from the Microsoft 365 $6.99 Personal charge. If you cannot upgrade your subscription plan from an in-app purchase, then you have two options:

1. Purchase the Microsoft 365 Family license from the Apple online store.
2. Microsoft's Compare All Microsoft 365 Plans where you can purchase the family plan.

I provided two different links that would let you purchase the Microsoft 365 family license plan. An Apple Store should be able to offer you the same thing as though you purchased it from either link.

Office 365 as you know is a Microsoft product, I think you should asking your question on a Microsoft forum.