Jump back and forth between the two, to maintain the chronological flow. Just be careful with POV -- maintain a steady narration. (meaning the distance the narrator is from the scene -- is he omniscent with one character only, or with all the characters. Head-hopping is easy to do, but very difficult to do well.) This is an instance where knowing your characters excrutiatingly well is imperative. Giving the speaking characters individual, distinct voices is the biggest challenge.