From what I have seen, the hens do not take turns. Multiple hens will sit on the communal nest at the same time. It can create a situation where the hatch rate is abysmal because they are trying to sit on too many eggs. Eggs get started developing and then get moved to the outer parts of the...
If a person keeps disturbing an active nest, the hens will abandon the nest to find a "better hidden" nest. If a person takes all their eggs from their nest, they will abandon it if fake eggs aren't left in their place.
A broody hen on her nest is a different situation. It is why they are so...
It's entirely possible that you heard the egg song. It's also possible that it is a communal nest and that none of the hens are broody yet.
Since they aren't your guineas, I would leave the nest alone.