There is no way to password protect certain Cloud files if you share your entire Cloud account with other users.
If you want to grant access only to certain Cloud file(s) and not to your entire account the other users must have their own MLO Cloud Sync subscription. Then you can share selected Cloud file(s).
How you can share Cloud file(s) in MLO-desktop:
1. Open your MLO file and go to "Synchronization"-> "Configuration" -> "MLO Cloud";
2. In the windows that appears click "Browse". Here you can choose an existing Cloud file or create new to share with another user;
3. Go to "Properties"-> "Sharing"-> "Share";
4. Enter the email address of the Cloud user you want to grant access to and click "Ok".
5. That user needs to create a new local file in his MLO and link it with the Cloud file that you shared.
Henceforth you both will be able to manage the tasks connected to the shared cloud file.