Each steam user has their own cloud, it’s not one big cloud…
We’re really not communicating here, eh? 
I know, for sure, with what I have, I can store different save games for each player. As long as they choose a username through a widget ( or whatever ), we’re set. All on the same PC.
Say I use my PC and choose username Clockwork, and you use my PC, and choose username Hairy. Then the code can use slot names:
Clockwork.save
Clockwork.extra
Clockwork.config
etc ( and, externally, Clockwork.config will be stored in Clockwork.config.sav ).
and you will automatically get assigned slot names:
Hairy.save
Hairy.extra
Hairy.config
All files in the same folder, no confusion. I can load the right stuff for the right user. Everything gets copied to the cloud.
If the different Steam users user different Windows usernames, it’s a bit better, but if doesn’t really matter. If they use the same Windows username, it just means that you can see my save games…