Unsophisticated users will probably be the biggest hurdle, so best to use a solution they understand IMO.
Dropbox would work surprisingly well I think, it supports headless installation via SSH, you can find that info here: https://www.dropbox.com/install-linux
Then it's just a matter of syncing it to a possible shared folder, or locally/individually etc... you get the drift.
I don't want to spam the support forums with links, so the first few results of this Google search should prove helpful for any further SSH-based configuration.
Worth a try, hope it helps!