How to use the Internet and vpn in the local network?

Question

VPN

There is a domain server with 3 network cards. the Internet comes to 1, the 2nd card distributes the Internet via dhcp through the Routing and Remote Access service. A cable from a provider with VPN is plugged into the 3rd card, where you only need to register ip and gateway. Accordingly, users have Internet from 2 cards. On the server through vpn it goes to the external device, but local users no longer have access. Pings only up to ip 3 cards. What and where to prescribe so that they have access to the outside through a vpn card?