Hi there,
Thanks for reaching out. I’d be happy to help with your question.
We have a premium extension called Event Aggregator that allows you to import events from various calendar sources. To sync the same calendar across all site, you could import the events from Google Calendar, and use that to manage your events.
Another option available with Event Aggregator is to import events from another WordPress site running the events calendar. You could use the main site to manage events, and have the subsites pull events from that.
Hope that helps! please let me know if you have any additional questions about this.
Thanks,
Sky