Steam is introducing ‘Remote Play Together,’ a feature that allows friends to join each other’s games online. With this update, only the host needs to own the game while friends can join.
You can join the steam beta here and then launch local multiplayer games. After launching the game, head to your friends list and select ‘Remote Play Together.’
Once your friends are linked, their controllers will act as if they’re plugged into your computer. You can then adjust voice chat and game volumes all in one place.
Remote Play Together can let friends play local multiplayer games online, stream their shared video, audio, input and voice between the placers, and you can even share the control of keyboard and mouse.
This is available on PC, Mac and Linux.
For privacy concerns, Steam will only share the game window, and your desktop will never be shared.