Network / Sharing :: QoS Ignored By Access Point Router

I am sharing my internet connection with my roommates, but lately they have been using P2P to download stuff which uses almost all the internet speed available. I have set up QoS to limit their bandwidth in the main Asus wifi router which directly connects to the modem, it works great for a few days, but then it doesn't work anymore, I still get slow internet speed now. Since my flat has 2 wifi routers, one is the main and another one is set up with a different name but still connects to the main router via the ethernet cable a few metres away so that the wireless range is increased. Just for your information, the two routers are transmitting on different channel, if you think that might be the cause and they have different SSID.

Could it be possible that the QoS only works in the main wifi router and doesn't affect the other wifi router which my roommates also have access to it?

I have changed the default router password so I am sure that they have no access to the router's settings.