How to organize backups on one BitTorrent Sync for multiple users? Or is it better to choose something else?

Question

linux

I wish you well.
There was an idea to run a small server on Raspberry Pi with a hard drive, which would be exclusively engaged in creating backup copies of files and storing them for demand. Initially, I thought to do everything on BitTorrent Sync, but now a problem arose: I was going to connect several of my relatives to this system in order to store their backups. As I understand BitTorrent Sync won't let me do it nicely; when adding new folders by other users, they will simply be thrown into the general heap. If I have 4 users with 20 folders each, then this will already be a terrible mess.
Maybe there are some better solutions? Or maybe BitTorrent Sync can somehow be configured to what I need?
Thanks in advance.