You can source all the calendar info from a single Google Calendar, or you can set up one calendar as the master, and have the other two calendars fetch off the master (using an ICS subscription).
Things of note:
1. Google fetches from a calendar once between every 12 to 24 hours, so there is always a delay. Also, new events in Google sometimes don’t update for an hour or so into its ICS feed.
2. You really don’t want Ai1ec updating hourly if you can avoid it, especially if you have a lot of events.
3. By default, only future events (based on time of fetch) are exported from Ai1ec in an ICS feed, so older events may not come across.
4. If the websites are on the same host, you may find that your webhosts firewall rules might block the site fetching data from itself (or even their local network, depending on their setup).
