The Vonage boxes are in-themselves also Routers....so You would have to go into the Vonage box setups and make sure to disable DHCP and such things that may well be impacting things....
Not sure why you need each PC to be chained thru a vonage box in the first place as the vonage box, once set up rarely need any adjusting, at that is the case here with my vonage box.
IF you reaally need the PC's to share stuff, you would be far better off having the PC's both go thru the 655 in the first place, and leave the Vonage boxes alone.