The way command eject works varies between aircraft types. In the Tornado if the front handle is pulled the canopy then the rear seat goes before the front. This is hard-wired through the ejection seat plumbing.
The rear cockpit can has an easy to select lever to either go on their own or for the front seat pilot to join them. In my time we always flew with 'both' selected but it was not always so with inevitable results.
In the Hawk T1 the command eject is awkwardly placed to the rear of the seat. The rear seat occupant can choose to go on their own or take the front seat with them. By contrast the front seat can go on their own and give the rear seat occupant something exciting to watch.