Lost Children Of The Big Three

There was a legend of three children, born to the same woman but. Each. Had. A. Different. Dad. And their parents were the Big three. Together they had infinite power. They could build Olympus higher or tear it down completely.

Sierrena, Elizabeth(Lizzie), Alexander Kayne are all siblings. But they are different. They are Demigods, but even then they are different. Each sibling has a different father. And each is a god of the Big Three, Zeus, Poseidon, and Hades.
Each child is powerful but together may be unstoppable, therefore more and more monsters attack. Eventually their presence endangers the camp. What will they do? Will they survive?