Is there any fast way to limit my brother's wireless internet speed without his knowing?

Yes there are a few ways.

1. On router, use OpenDNS. Block some sites – beware there is a warning page with a click to email you button..

-Block 53 UDP to external sites

2. If your router supports access controls, there may be options here.

3. Compain about mother in law. Then you can have all the bandwith to yourself in your new place.

Hello, See if you can make a second SSID (Wireless network), If you can make it hidden (Dont broadcast), Then see if you can limit the download speed on the first network and browse faster on your hidden one

When connecting to your hidden one on a Mac you will need to press Join Other Network, Not sure on PC

See if your router has QoS. If so, set your machine to a higher priority, and his at a lower priority. If your router has no QoS, nothing you can do....