[X] Move to save the squad of Town Guard, the Mechanicus should be able to manage those genestealers with advanced warning and you might be able to rope the guard into your own forces...
[X] From what you remember the largest portion of Nortrain's citizenry are fleeing towards the main road leading towards the Governor's Keep, it's a few roads over and should be easily reachable if you head straight there. Though whether you can calm such a tide of people is a bit of a gamble, but... if you don't try then it's hard telling how much damage the Fourth Generation scattered within might wreak...
[X] Intercept the Fourth Generation in the crowd and excise them, you cannot risk that the temple's own response isn't fast enough to save anyone that these broods may harm.