Hey Carl,
Thanks for reaching out.
What you describe is unfortunately not possible in a straightforward way 🙁
You could technically pull this off with either of these two options:
• Manually import and export events across all three sites.
• Use one of our other add-ons too, called iCal Importer, to take the iCal feed export of the “main” calendar and then run imports on a schedule and/or manually on your two other sites. You can learn more about this add-on, and how its importing process works and such, on its official product page here → https://theeventscalendar.com/product/ical-importer/
I hope this information helps!
Sincerely,
George