I'm no GV expert, but I don't believe that GV supports "call-forking" to multiple endpoints. However, what you are asking is easily achieved with two OBis.
Set up your second OBi as an independant device with its own Dashboard etc. If GV is on sp1 on your original OBi, then set:
Voice Services > SP1 Service > X_InboundCallRoute:
{ph,pp(ob200123456)}
Where 200123456 is the number of the second OBi.
You can set a delay so the second OBi only gets called if the first OBi does not answer the call say within six seconds in this example:
Voice Services > SP1 Service > X_InboundCallRoute:
{ph,pp(ob200123456;d=6)}
This method uses the OBiTALK network to fork the call onto the second OBi. Call forking to up to four devices is allowed.