I'm not sure about op, but I actually run Lancache (lancache.net) locally on our network. It supports Steam, Windows Updates, Epic games, and pretty much anything else served over http.. (https://github.com/uklans/cache-domains).

This is all assuming you're not using a domain etc.. and have any of the myriad of other tools setup. We run lancache strictly for the fun-net segmented network.

I maintain a primary disk image with all the games installed. During a party, all the machines boot from that same image, except each with a private copy-on-write overlay. Any changes made on a machine are written only to the overlay. At the end of the party I delete the overlays. The primary image remains in exactly the state it was in before the party.

So before each party I just have to install updates on one computer, like a normal person would. No need for a special cache. (Or arguably, the primary image is the "cache".)

Full details and code in this github repo: https://github.com/kentonv/lanparty/

Gotcha, so if there was a big update during a party you'd have to either let everyone update themselves; or delete their overlays, download the update to the primary, and then make new CoW overlays for everyone.