Wasn't incest involved? My knowledge of Egyptian myths is nowhere near as abundant as that of my Greek myths, but if I recall correctly I think incest was involved in some way.
Most of my knowledge of Egyptian mythology comes from the Kane Chronicles, I think the simplest explanation is that the myths changed drastically throughout the history of the Egyptian empire becoming one thing or another as the society evolved. Though yes most of the gods had kids with their siblings, it was creepily normal. Geb and Nut, Isis and Osiris' parents were brother and sister.