For spirit beasts, enduring the effects of the formation array was impossible, even for a second. For the two brothers, it was nothing short of a miracle that they remained unaffected. However, as they hovered on the brink of death, they inadvertently discovered a loophole in the array's design.
The formation array had a specific technicality: it only targeted those who were alive.
Because the brothers were on the verge of death and their souls had begun to leave their bodies, the array failed to register them as living entities. Moreover, since their near-death state wasn't caused by the array itself, their souls were not swept away like the others.