Can multiple people hallucinate the same thing at the same time ?

[Angrboda]

Generally speaking, explanations, particularly scientific ones, are meant to explain classes of events, to find regularities over a broad range of instances.  It sounds like you're looking for explanations of specific events or instances.  Given that the explanations are generalizations, they are not necessarily going to explain any specific instance.  There's a mismatch in trying to find explanations for specific events using generalizations which will always be unsatisfying.  This is one of the appeals of anecdotes, which, by their particularity, will always escape definitive explanation using general laws and regularities.  Take the miracle of the sun at Fatima.  We can postulate that any number of general mechanisms might have been at work at Fatima and might explain the appearance of a miracle, but we do not have enough data about what exactly happened at Fatima to say that this or that explanation was definitely at work, and as such we can never fully rule out the possibility that an actual miracle occurred.  This can be a form of defense used to protect the miracle.  By examining each general phenomenon that might explain Fatima, because they don't necessarily apply to this or that piece of evidence, each general law can be discarded one-by-one until the only known explanation still standing is that of a miracle.  Unfortunately for such a defense or apologia, that argument is an appeal to ignorance and therefore is invalid, but it can be convincing to any who do not recognize that flaw, or who are persuaded in spite of it.

Yes i still know that when 2 people say that they have witnessed a ghost of a baby boy and they explain him to the smallest details the most probably answer is still that they are lying or were under some sort of a delusion that maybe science still doesn't understand very well , that would be the most rational answer to those stories.
Or in the second story where the whole family kept seeing their dead grandmother for months in their home the most probable explanation is that they are all lying or were all under a delusion , but for me it's impossible to just discard it as something trivial , i think there is a real phenomenon going on there , whether it's mass delusion and experience of the same hallucination or a real ghost ( whatever that means ).

Well, it's not clear that you understood my point, but regardless, let's cut to the chase: what do you think you should conclude if there is no explanation?