Multiple users sharing files

Aha, now we are onto something. Switching to SMB alone seems to have cleared up our permissions issues. I'm not sure if this is due to AFP trying to be smart and match up local system permissions with remote server permissions or what, but over SMB the proper permissions and ownership are retained and even without setting up additional restrictions via Windows we are able to have multiple users reading/writing from mixed-ownership folders and files, which is exactly what we needed.

Thanks for suggestion to switch to SMB, mdgm!