How to sync multiple calendars

To sync two Google calendars that are owned by two G Suite/Gmail accounts ( for example, work account and personal account), you'll need to give one of the G Suite accounts access to the calendar of the other G Suite account. 

To do so, go to your Google Calendar, click on the "+" next to "Other calendars", then click on "Subscribe to calendar", and type in the email of the other account:

Once done, then create a Vocus.io Calendar. When you create or edit a Vocus.io Calendar, in the creation wizard you will be given the option to have both calendars synced.

For more info, check out this Google Support article.