Reign nodded at the four before taking out his sword and decapitating them. Wolf used his flames to envelop their dead bodies and burn them down to ashes before the two left the room, leaving the door open so that the ashes would scatter in the prison.
Reign had promised the four that he would spare their souls if they told them everything they knew about the base. They had fulfilled their ends of the deal, and Wolf and Reign made sure that they didn't lie. Reign had used his ability to grab a hold of their souls, making sure that Aethion was able to sense it together with him.
Any lies they spoke would be picked up by the two if Wolf didn't pick up on it beforehand.
Of course, there was no saying whether the base would be the same inside as the elders had said. Both Carlos and they had told them the same things about the inside of the base, it was always different.