open up your browser and type in 192.168.1.1
a password prompt will come up. Leave username blank, type in 'admin' (without the '') as the password.
After the screen loads, go to advanced
goto forwarding
Open up steam, goto play games, right click on whatever game you'll be playing, click on "Create Desktop Shortcut".
At the end of the target line add "+clientport [porthere]" replace [porthere] with the port. in the example i used 27006.
click okay. goto start>run type in cmd
in the prompt, type in "ipconfig" and take note of the ip address. This isn't your real ip address, its the ip address assigned to you by the router. take note of it.
go back to the port forwarding, and forward the port to that ip address.
the port I used was 27006 and my DHCP ip address assigned to me by the router was 192.168.1.100 so it would look something like this:
for your brothers computers use different +clientport [porthere], then forward that port to thier computers. For example, my brother has the ip 192.168.1.101, and for him i set +clientport 27007. So i would forward port 27007 to 192.168.1.101 via the port forwarding section of the router.