Connecting RPI to shared VLAN through VPN over LTE/4G?

Many ROV-developers seem to be looking for a solution on how to connect their vehicle to ground control over LTE/4G. I have tried setting up a VPN server (Algo VPN) to which I connect the vechicle (the Emlid Raspbian image) over a 4G shared wifi connection (Android phone). The RPI can talk to the VPN server and I can SSH to the RPI from the VPN server.

However, I would like all clients connected to the VPN server to be able to talk to each other in order to run e.g. Qgroundcontrol mission planner. I guess this involves setting up routing rules for the clients. Has anyone done something similar? How did you do it?

I managed to put it together by modifying firewall and routing rules on the VPN server. Now it is possible to have all devices communicating on a virtual local network over the internet in a secure way. Here is a link to the modifications I made to the Algo VPN server: Add documentation for client to client communication · Issue #640 · trailofbits/algo · GitHub