The warden triggers an alarm that opens all the cell doors and alerts guards in nearby areas. The cell doors open so that the guards can attack the prisoners. You don't want this to happen.
So, take out the scrying eyes and the guards. Then attack the warden when she is far away from the levers and block her path to them. After that throw in the hammer to Wulbren or open the path from the oubliette. Do not unlock the cell doors, because then they will try to escape towards Moonrise Tower and run into the guards and get wrecked.
Thanks.
Keeping the warder away from the levers was the thing.
