In the router, TCP Port 1723 (for a pptp VPN) should be port-forwarded to the Host computer's Local IP address. This number will likely be the 192.x.x.x referenced in the picture.
No worries. The WAN I mentioned finding will be the same thing that all the clients connect to. They will also all connect to the same host VPN server. (I assume. Your company may have more that one) You will only need to forward 1723 to the Host server's local IP on the network. To re-cap:
user 1, 2, and 3 will all connect to the WAN ip address.
The network that the VPN server (Host) is on should have TCP 1723 forwarded to the VPN server's local IP.