I somehow doubt Kleiner and Eli's importance in the conflict. I mean, they have just managed to escape Black Mesa, how on Earth will anyone know what role they'll play in events to come? The main focus, if you play as a human should be Breen and the steps he took to persuade what was left of the government, the power he gathered in the crisis and the final surrender.
He surrendered his own species to an alien empire, allowed them to turn our cities into prisons, send people who resisted to processing plants and off-world, watched as Earth was turned into a wasteland and for his efforts gained scientific knowledge of the world beyond.
