Networking and internet in general is a real pain to configure (I say this out of experience). What you can try to do is this.
1. Go to your brother's pc.
2. Go to start (bottom left corner)
3. Type CMD in the search field and press enter.
4. Type ipconfig
5. Now join the ip in the ipconfig on your own pc. (would probably look like this: 192.168.1.XX)
Assuming you are not on different subnets this should work. If this doesn't work and you are on the same network try to turn of "discover devices" in your network centre and make sure the connection type is on "Home network" and not on "Public network".