Is this manual or automatic failover?

I dont think if this manual failover then one database failover to mirrored will support for all you need to manually need to failover the rest of DBS.

Incase if you sre setting up the automatic dailover with withness server then if the withness server does not receive the pingdom from the pricipal serevr then it will initiate failove for all the databases which are participating in mirroring.