On Steam, there are no multi-seat licensing. Although Valve does do this for cybercafes and education institutions, it is essentially the creation of multiple accounts (one account per computer) with licenses applied manually by Valve that are simply logged in automatically when the computer starts, which is the same as multiple single-user accounts.
To simply put, in order to achieve what you're talking about, simply do this:
- Create a steam account for each person (or workstation) you would like to play.
- Purchase the game that you would like to play for every single account.
- At each workstation, log into a different Steam account that you have created for this reason.
As for maintaining updates, there are many solutions for that. What I typically do is have the files sync from a central computer/server. For BYO computers, I put them in a network share and ask everyone to copy from there (as opposed to having everyone download altogether*).
Steam is supposed to be a single-user based licensing system. Alternatively, if you want each user to BYO their own Steam account, you can simply purchase licenses to 'gift' that can be activated on their own account.
*Not a good idea, unless you have super-fast internet, and I mean several GB per second (cumulative).