Setup openvpn and use it as a router

General setup:

https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-ubuntu-16-04

Static IP:

https://dnaeon.github.io/static-ip-addresses-in-openvpn/

Topology:

https://community.openvpn.net/openvpn/wiki/Topology

Port forwarding:

http://superuser.com/questions/927060/openvpn-server-to-forward-incoming-connection-to-client

See also: http://unix.stackexchange.com/questions/55791/port-forward-to-vpn-client