Sorry for my late answer, I've been too busy
So, I get what you're saying about sharing each folder individually - I just tried playing around with it and I can't see how I'll get "Camera backup" to automatically upload pictures toe the path I've shared from the server, where the original folder with all camera backups are located.
Is it possible that you can point out how and what to do, before I do something and mess it all up?
(Situation is still: I want to backup my pictures from my phone when they get taken and upload them to my NAS - this will be done for 3 devices in total and I don't want any of the other devices to be able to view and/or change each other backups)