Again, you cannot tell if someone is downloading two different files from the same server (like happens when you open a web page and it has multiple images and CSS files) or the same file via two connections.
You can limit the total number of connections a user has, but limiting every user to one total connection against a unique destination IP is completely unreasonable. It would make websites load incredibly slow.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.