In a Hawk with command eject 'on' the rear seat firing will then start the front seat ejection sequence,if command eject selected off then both seats fire independently.On a training a/c (say Hawk) it was designed to have the instructor in the back seat which is why I commented previously that if carrying a passenger in the back seat then the command eject would probably be turned off.
On an operational a/c then the command eject may work both ways !