I agree that the story of Moses in the Bible is a mish mash of older stories that were already in the Egyptian tradition (and other ancient traditions like that of King Sargon). The story of the baby being drawn from the rushes by a princess (or goddess) for instance was already around.
The family of Pharaohs of the line of Thutmoses, i.e. of King Tut fame, were real people in history their mummy's being on display to see. I've always found the Thutmoses and Moses name similarities curious. One family member of that line, Akhenaten (who's mummy has never been found.........he's referred to as the heretic Pharaoh) introduced a mono theistic religion based on sun worship (the At en). Of his mummified family members that have been found, one of interest is his grandfather Yuya. Although not of royal origins but married to one of the Tutankhamen line, he was buried in royal tombs AND FOUND! http://en.wikipedia.org/wiki/Yuya It Author Ahmed Osman wrote a compelling book suggesting that Yuya was indeed Joseph of the Bible. I really enjoyed reading that book Hebrew Pharaohsof Egypt although not agreeing with all his ideas.....still compelling.
(There was no correlation made with the Ya in Yu-ya's named but I noted it.)
Both Yuya and Joseph of the Bible were said to be masters of the chariots and 'Father to a pharoah'............coincidence? Maybe. The main point that detractors made about this idea is that the Bible says that Joseph's remains were exhumed and returned to the land of his forefathers and Yuya was found in Egypt. Well................I say the writer of that little piece of fiction hardly imagined that the mummy might be found 3,000 years later in Egypt!
So, if after several hundred years have gone by and some old Jewish older man at the gates wants to tell a fable to establish some point to his listeners of interconnectedness or whatever...........he only needs a general framework and from there weaves the tale. Those Bible writers I'm pretty sure had no thoughts whatsoever about who might be reading or telling the tales 3,000 years later.
Even if Yuya was not Joseph, the story of his and his wive Tuya's discovery is fascinating!