Riyas,
I just configured an OBi as close as I could to your OBi #1 configuration (SIP on SP1 and VG3, and Google Voice on SP2). The VoIP provider and corresponding DigitMap I used on VG3 were not the same as yours, obviously, but that clearly shouldn't matter. Along with a second OBi as OBi #2, I implmented the configuration details from Reply #5 of this thread into both OBi's. The call routing from OBi #2 to OBi #1 worked exactly as expected.
I don't know what's going wrong on your end, but the concept works.