Linking all your calendars in FreeBusy is really simple:
Go to Link another calendar
Provide the email address associated with your calendar.
Confirm provider and sign in.
After you sign in with this calendar, it will be automatically linked to your account.
To see which calendars you've already linked, visit the Calendars & Integrations page.
Note: FreeBusy combines availability data from all your connected calendars. You can share your availability using any email address that you’ve linked. We’ll always show the same availability regardless of email address used.