If you have multiple computers on a LAN and you're using Steam, you should be able to use family sharing to spread one copy of the game to all of them; however, only one computer can be online on Steam at a time with that game.

https://www.cnet.com/how-to/how-to-share-your-steam-gaming-library-with-friends-and-family/

https://www.youtube.com/watch?v=woQNyEuoaIw