I think I can help now that I got my disclaimers out of the way...
There would not be selective sharing of individual folders or parts of the .mlo file. Instad you would have a different file for work stuff than the file for personal stuff that you don't want to share.
Then the mlo cloud account could serve only the work file, and they would syncronize with the whole file. That's how it works that I know of, but I haven't used cloud sync since my free trial many years ago so I don't remember how you control which files to sync.
I also don't think there is a multi-user login for a single account, right? So it would be share the credentials and then they can connect to sync. All who log in would own it just as much, to do whatever changes they feel like. Because from the perspective of MLO cloud sync, they are you.