GTM switch multiple VS IP at the same time

There is no way to group endpoints as you are describing as the design was based around all those resources monitoring the same thing and therefore changing at the same time. If you'd like to have control over when the items failover, one way to do that would be to set the pool monitor to gateway_icmp (to provide you with the highest chance of returning available regardless of functionality) and disable the pool whenever you would like to manually failover. You would only need to change the primary site pool as it would take precedence, if enabled.

The F5 system is designed mainly around automatic failure so solutions that bypass automated failovers are more of a workaround than anything.