How to create a virtual network to play single player with my friends in the same game?

i guess start by using virtual local area network software
https://www.google.com/search?q=virtual+lan+software

then use tcp-ip multiplayer mode in-game to create/join

Software I can recommend is ZeroTier One or Radmin VPN
If you connected, you treated like you're on same LAN or network so you can use ingame TCP/IP game