Three Calendars - Appointment in one does not block time in others

I have three calendars for services provided in three different ways: two different geographical locations, and online services offered in both. The calendars for the geographical locations are active for different days. The calendar for online work ought to be available for clients in both geographical locations. 

However, if an appointment is book for Location 1, that time ought to be blocked for the online service. I can't do In Person and Online at the same time, after all. 

I have double checked everywhere in as far as I can trace, but the Online Calendar and the Geographical Locations Calendar seem to not block each other. How can I fix that?