...but how could you question what so many people saw?
Don’t question the validity of the statements of the people from the story, question the story itself because the very basis of the story is absurd. If the sun were to have danced, people other than those at Fatima would have seen it. The ways in which people can delude themselves or simply lie are legion, and a powerful religious setting like this one is a prime candidate for it to happen.
I’ve heard of this story mentioned a few times in discussions with religious people and they all take it as Biblically true, even though there is zero evidence for it. None of them seem capable of thinking about any aspect of it other than the stories told by the masses. It’s supports their beliefs and that’s all that matters to them.
*Edit errors due to my lack of knowledge of the event*