can i use my brothers cd key

[Spiko]

can i create a cd key that my brother is using and still go online

Edit i am on ut3

[VoodooMaster]

You can use your brothers CDKey but you will not be able to play online at the same time as he is.
But you both can play on LAN as long as you don't login to your online profile.

[ShadeMistress]

You could use the same CD key, I believe. Just know that only one of the two of you will be able to log in and/or play online.

You'd be better off saving a little cash and just buying it... it's only about 20 bucks here, 30 for the Collector's Edition with the DVD tutorials.