Thank you for reaching out!
Could you clarify if you need to join these networks?
This seems like it would be a perfect setup for OpenVPN TAP mode. This mode basically operates as a switch, joining up these networks. This way all of the devices will be able to reach one another.
To configure the OpenVPN in TAP mode, I'd recommend checking out our article on how to bridge two offices' LAN networks. Please keep in mind, that if more than one client will be connecting to the server, then TLS authentication will need to be used.
However, if this is not an option, then consider using port forwarding, as NAT is enabled on our routers by default.