There was an interval of "an entire night" in the battle where Magneto left to recruit the villains, and other characters were hidden (those not hid "evaporated before our eyes", according to Kurt and Scott), protected telepathically by Quentin, who was strong enough to block telepathy Red Massacre, and apparently the technology of Sentinels.
After resting ... they came back to fight ... and were simply hidden from beachfront Skull and Sentinels.
The tie-in of Magneto ended the saga. haha