In the books I read concerning the Egyptian myths, I found that though not extensive, the gods and their stories are very complicated.
The importance of certain gods seemed to wax and wane depending on the period of history as well as where you were from. Ra was important to those in Heliopolis for example. This is further confused by the fact that other gods would obtain some attributes of the sun as they grew in popularity: for example Ammon-Ra, the king of the gods during Egypt's empire building days. Sometimes Ra is Ra-Herakty. He also has three forms:Kepri(dawn), Ra(noon), Atum(sunset).
Every time I read the story of Osiris in a new book, there is always some new detail that was added, while another detail is missing. Did Isis get pregnant with Horus by resurrecting Osiris, or just his penis!!! Did she reunite his parts and mummify Osiris after he was cut up by Set, or did she bury each piece where she found it? Did Ra defend the acts of Set because he needed him daily to defeat Apophis, or was this job given to Set as punishment for his evil acts? No doubt there are different traditions, but it is enough to make my head spin.
The Egyptians did not give us a complete, coherent picture of this most important story that reads from beginning to end unfortunately. Plutarch, the Greek writer did that, but he left out alot of details that have to be pieced together from what the Egyptians themselves left.