The Cast is a mess.

Actually watch The Ten Commandments with Charlton Heston and Yul Brynner as Ramses II. Brynner was an exotic-looking and much more commanding Pharoah. I don't know what Scott was thinking casting the very common-looking Joel Edgerton playing Ramses as a whiny weakling.
I liked John Turturro as Seti I. He is at least a little more like an Egyptian. See depictions of
Amenhotep IV/Akhnaten. In any case his role was little more than a cameo.

Not always, although at various periods, they were. The Nubian Pharoahs were black.
Nubia also had its own pharoahs at Napata and Meroe, and many of its cultural customs and rituals were similar to those of Egypt. They also built pyramids.
Queen Tiye, the wife of Amenhotep III and mother of Amenhotep IV/Akhnaten, Princess Sitamun, and other offspring was Nubian. In depictions of Tiye and her son Akhenaten, as well as the daughters of Akhenaten, the African heritage is evident, while those of his wife Nefertiti depict Caucasian features. The Ptolemaic dynasties were Greek.
There was probably intermarriage also, but to keep the royal blood, whatever it was, pure, rulers usually with a few exceptions married a sibling to produce the heir to the throne. Secondary wives and concubines, of course, did not need to be related, as the children they produced would not need to be related to the ruler, and in most cases, would not ascend to the throne..

years later Netflix corrected this faux pas by making the Cleopatra biopic starring a black lady