Appointment type with two calendars?

I have an appointment type that would need the availability of two staff members. How do I go about doing that? For example, when customers book a couples massage I need to have two therapists available - how do I create an appointment type that would allow for that?

You'd need to create a "Calendar". Go to "Scheduling" -> "Calendars", and create a "Calendar" with the appointment type. 

Next, go to "Scheduling" -> "Sync With Other Calendars". Add the relevant people in "Select a Calendar". Save it, and you should be good to go!