in simple steps :

1) download and instal on all workstation Cannon Brawl
2) download and instal Sandboxie from official site http://www.sandboxie.com/index.php?DownloadSandboxie
2.1 ) if you use steam exit on all worksation
3) Run on first workstation Cannon Brawl them go to Settings > video and set window screen (check picture)
4) First player can stay in game. Second do the same thing but before launch Cannon Brawl Run steam by Sandboxie -> login and choice your game
4.1) Or if you hawe that game without steam just run by sandboxie
5) thats all enjoy your Epic fights 🙂