When Fraying Omnipotence resolves, first each player loses the appropriate amount of life at once. Next, the player whose turn it is chooses an appropriate number of cards in hand without revealing them, then each other player in turn order does the same, and then those cards are all discarded simultaneously. Then, the player whose turn it is chooses an appropriate number of creatures they control. Each other player in turn order does the same, knowing choices made by previous players. Finally, all of the chosen creatures are sacrificed simultaneously.