Calendar - Cannot change invite to a shared calendar

Hello, my and my wife have a shared calendar, of which I am the owner, called "Family".

Occasionally her friends will send an invite to her iCloud account and it shows up in her calendar, but she is unable to change that invite from her personal calendar to our "Family" calendar. The option is greyed out.

I have ensured she has edit access and she can create events on our calendar with no issues, it is only events that someone else sent (they also have iPhones) that she cannot change to our shared calendar.

I have tried and messed with setting on both iPhones and MacOS.

How do we fix this?