PC Online Multiplayer Gaming - How to connect like couch co-op?
Solution 1:
Try Parsec . It allows for low-latency couch co-op through mirroring your sons PC on his friends and has full controller support. Setup on host and client ends are super simple and it has support for mac and linux too. This does mean that the game being played needs to support local co-op, like Cuphead or Spelunky. I play Super Smash Bros. (through emulation) with my friends using this method and it works well. I know you said to ignore Steam, but Steam has its own remote play function that it implemented recently that works similarly to Parsec, though I haven't used it enough to give a fair comparison.