Hey Michael,
Thanks for reaching out!
If you are trying to have this happen more or less automatically—in other words, you don’t want to manually be importing events from A and B to C on a day-by-day basis—then unfortunately the only solution for that would be our iCal Importer plugin.
Each calendar generates a feed of its events. If the Events page URL is site-a.com/events, the feed URL is site-a.com/events/feed.
So with the iCal Importer plugin, if you want events of A and B to imported to the calendar on C, you would install the iCal Importer plugin on site C. Then, you would add recurring automatic imports for both feeds of Site A and Site B.
On the interval you set, Site A’s feed and Site B’s Feed will be queried for new events, and if new events are found, they’ll be imported into Site C. 🙂
I hope this explanation is clear and helpful—check out the iCal Importer’s product page for more information on this process I described above! → https://theeventscalendar.com/product/ical-importer/
Thank you,
George