We finally managed to play all together (over ESO). Why can one guy join but a second one is too much? What's up with the networking, it's not that hard. They tried to directly connect, but didn't find anything, with and without port.
Used the OverrideAddress='x.x.x.x' launch option with my public IP.
Friends can see my lobby among LAN servers, but can't join. Used the OverrideAddress='x.x.x.x' launch option with Tunngle adress, with and without hostPort=2301 after it. It doesn't matter who it is, as long as there's already one in the lobby, the other can't join. One friend can join, the second one can't. I port forwarded port 80 for TCP and ports 2300-2310 for both TCP and UDP.
