Complete noob to Linux groups: can it be set up that files created by a user belong to a group s/he is not part of?

I host a few people's websites on my servers. I need to give write access to their files to a group of maintainers who I don't trust with root access.

I basically need all files created by, for example, the users foo and bar to belong to the group baz, but I don't want foo or bar to be in that group (since this poses a security risk that they could edit each other's files).

Is this at all possible? Am I even making sense?

Thanks.