All is made clear,regarding Abraham and Sarah's traversal into Egypt, when we realize what biblicists meant by the term "Egypt." As Ralph Ellis so brilliantly points out, the name Egypt was employed by the composers of the Old Testament to denote Thebes in Lower Egypt. This was the city and region controlled by the adversaries of the Hyksos. It was considered a separate region, with different rulers, gods, customs, and politics. So, it was not the country of Egypt that Abraham visited, but Thebes within Egypt.
Michael Tsarion