For on disk deduplication, Steam supports user-specified locations for installing games and dependencies like Steam Linux Runtime. 2 users can theoretically use the same Steam library at the same time. To evade issues, auto updates should be disabled in the Steam clients. Steam doesn’t support completely disabling updates afaik, the best is setting update period to 3.00-4.00 AM. DXVK cache files must be located outside the Steam library folder. Otherwise if 2 people play the same game with Proton at the same time, cache files may be corrupted. (the default is the folder with game exe) Info on changing cache file location: link