I have bought three copies of the game and don't have a problem. I installed twice on my computer and the third on my wifes. We are able to play together with no problems and when she is not playing I can switch to my other character. Try this. On your computer log in to your steam account. Right click Arma II Select 'Launch Arma II Combined Operations' You should briefly see a DOS window pop up. This is where steam is inputting the correct CD key in the registry. Let game load then exit. Launch DayZ the way you usually do. Have your brother log into his computer and his steam account and follow the same steps. You should each have the correct CD key now.
