[iControl Rest]Is there any way to get the current active device and next active device name of a traffic group

if you hit: https:///mgmt/tm/cm/device/

You will get a JSON dataset that within it has (for us the pair of F5's) each F5 in the HA, and under each F5 there is a value failoverState

so for us in php reading the variable it's $JSON["items"][0]["failoverState"] and $JSON["items"][1]["failoverState"] for the failover state and $JSON["items"][0]["name"] for the device name.

Hope this helps