A cheap router would do the trick, but you can also give yourself higher priority with the QoS service, and make your brother's connection suffer when you are using the net, but dunno if that's gonna work with your configuration or not.
Yea I know how to view the entire image, but this doesn't says much because I don't even know your upload/download speed or the quality of your internet connection, etc...
I just googled the "QoS Packet Scheduler" (I never used it tbh;]) and perhaps I was wrong when I said it's might help, it's not the same as the QoS in the routers... this needs a little bit more reading:)
edit:as I said, a cheap router would really do the trick if you want to prioritize traffic.
pics says brother uses approx 1000 Bytes/sec, it would be a really shitty connection if that would matter, but pics also says that the quakelive gameserver gets 3550Bytes/sec ....so I'm confused:)
and pingtest.net to the location where the server was? Only the jitter what's really matters, but you should test things at evening/night when more people are online.
edit: also tracert that quakelive-hostedby... address.