The two elders knew that the demonic beasts were about to attack. They were very concerned about Zhao Hai. Not only was Zhao Hai their disciple, but he was also a cultivator with an innate Dao body. They couldn't let their guard down against such a person. He was the future hope of the tyrant's blade school.
Therefore, when the sect found out that the demonic beasts on the mountain were moving, they had been monitoring them all the time. Therefore, before the demonic beasts had finished gathering and rushed out of the mountain, they had already known.
However, for the sake of the sect's plan, they didn't inform the cultivators in the sect in advance. However, the two elders were afraid that something would happen to Zhao Hai, so they had come to yuanyue peak early. Therefore, they had seen everything that Zhao Hai had done.