I am currently trying to use Google Drive for exactly this use case.... I have synced my Savegame Folder to Google Drive and shared that with my friends, but now I am having the problem that I cannot overwrite existing savegame files anymore ("could not write to disk").
I can save into a new file without problems though, which then shortly afterwards appears in the cloud drive, so that my friends have the latest version of it automatically.
But why can't I overwrite existing saves anymore? Is it an issue in the game or does windows cause problems? Doesnt make sense to me that I can open e.g. a word document from the cloud, edit it, overwrite it without problems, but not a savegame.