We are sharing an internet broadband connection with 6 users at a place we live. We get 20 gb fup ( Fair usage policy) with 2 mbps speed from the ISP after the 20 gb is consumed the speed comes down to 512 kbps very difficult to browse any page.

The problem is we cannot track which user/mate is downloading and ending the FUP. it is very difficult to track so is there something that we can allot per user some amount of space like 2 gb of downloading or restrict all from downloading so that we can utilize all the fup till the end of the month. 

We are using this connection as wifi configured. A adsl router is configured as wifi and we all using all 6 laptops. No PC. 

Any help would be appreciated. I apologize if i am not clear with my question.