Hi Craig,
Thanks for getting in touch! Just to clarify, are you looking for a system that will allow you to import events via API from multiple websites onto a single site powered by The Events Calendar (or Events Calendar PRO)?
Unfortunately, we don’t support custom API event imports with any of our plugins at this time. A possible workaround might be to export events from your original sources to a Google Calendar, then set a recurring import with iCal Importer to bring the events from the Google Calendar into The Events Calendar. Would something like this possibly work for your needs? 🙂
Let me know if I can clarify anything or there’s something else that you’re looking to do here! Thanks again for stopping by!