As far as I'm concerned you all can regulate it amongst yourself. If you can find a way to punish/ban/block offenders please do tell.

Just a hint though, its probably inevitable that some people will attempt to vandalize this a lot upfront, if you realize this will only get boring for them after a while and save progress as it is made, eventually this will die down.... once that stage is achieved you only have to worry about occasional vandalism, which can be prevented by periodic backups. People do this kind of thing for attention, simply ignoring it and consistently reloading things from backups will fail to give them the attention they crave and they will go elsewhere looking for it.

If things don't seem to do better in a few weeks or a month, I can always make another spreadsheet and circulate it within a closed group or investigate a more robust system -- which I would prefer not to do.