Family Sharing Cannot Complete Errors

I am trying to set up Family Sharing for my wife and I.

I have created the family, as the organiser, and sent my wife a link to join the family sharing. However, my wife cannot complete the action on either her iPhone 12 or her MacBook Air 2019, both with the latest updates.

If she attempts to join, she is given the option to Cancel, Decline, or Join Family, but when she does click either Decline or Join Family, it inevitably says An unexpected error occurred or Cannot Complete Action, respectively.

If she attempts to set up her own family, she gets a Cannot Complete Action, error, on both her devices.

If I attempt to Revoke my invitation to her in System Preferences, I get a This Invitation Cannot be Canceled, error.

I've restarted all four devices that we have and still the problem persists.

We can both log into iCloud in System Preferences on both our devices and through Safari. There are no warnings that need to be heeded or old family sharing groups we were part of previously. I'm struggling to understand the problem. Please help and thanks in advance.