Group Quotas enable limitation of how much data a given group can write to a volume. The .quota.group file at the root of a given volume can be used to control quota settings.
Note: the .quota.group file is hidden (as can be seen from the leading . in the filename.
The edquota command can be used to enable Group Quotas on a per-volume basis. In this regard it is important to remember that an AFP mount is considered a volume to the client systems. Each different AFP Share Point is a separate volume to the client system.