If the VMs can't ping even between themselves, then something is definitely broken here, and it's not related to the RRAS service running on the host; regardless of their default gateway's behaviour, machines placed on the same network and with proper IP configuration should be able to talk at least between themselves.
Did you try disabling Windows Firewall on the guests?
Also, as per Greg Askew's suggestion, I'd try removing RRAS on the host; maybe it's messing up something with Hyper-V networking.