FortiAuthenticator High Availability Active-Passive Design/Behavior

[rickas27]

I'm trying to design topology for a 2 FortiAuthenticator system (in geographically separate areas) with Active-Passive HA.

Can multiple interfaces be configured for the heartbeat in case one pair of interfaces goes down (e.g. a cut cable)?

Can an interface that is configured for authentication also be used for heartbeat?

What happens if the heartbeat(s) go down but both FAC are still online? Will there be split brain? How is a split brain resolved?