Itachi and madara probably didnt jump from no sharingan to 3 tomoe neo i was just saying i wouldnt be surprised that they did
i would agree that it may have been hashirama's cells but kakashis developed in the same way without hashiramas cells
so either they somehow have a link, e.g. they develop at the same time
or the more likely explanation is that
no matter what tomoe you are at it will jump to 2 3 tomoe then ms straight away if you have a traumatic experience.
the death of a close friend or someone of that emotional attachment triggers ms activation.
you say why we havent seen itachi or sasuke jump from 2 tomoe well we dont know if itachi didnt
we know sasuke went from 1 to 2 to 3 to ms
but sasuke didnt have his closest person die at 1 tomoe or 2 tomoe...itachi was the closest person (despite that he hated him, he was still the closest emotionally)
his clan died but still none of those people not even his parents were as close to sasuke as itachi was, sasuke awakened 1 tomoe sharingan that night but if itachi died, he may have even developed ms, we don't know