You can do the same with your game traffic (you can mark it by selecting the game port), and create a new queue without bandwith limit, and set priority to 1
By doing that, your can play fine and your brother can download 
You could also mark http, voip, etc connections.
That connections will have highest priority and, if there’s enough bandwitdh, your brother can use it for torrent
But if you prefer to block all torrents, you can follow that: http://forum.mikrotik.com/t/block-torrents-p2p-traffic-100-working-on-all-versions/54137/1
Regards