If I'm parsing this correctly a Captain MC is the child of King Senhotenre's brother in law. Who had a daughter with Senhotenre's sister, who herself has (possibly male, possibly adult) children. If there's a grandson of Senhotenre through the female line is that a near enough connection to the previous dynasty to be a threat to Narmer if people become unhappy enough with his rule?
In theory, yes...
But also no.
I haven't decided yet how many children captain's sister has, or their gender, but if your MC is interested in learning about their father and any potential family, I'm planning to put in a scene at the end of the book where you can go meet them with your RO! (I'll come up with the children count by then)
So in theory, if captain's sister has a boy, then that boy was born after or around Senhotenre's death, otherwise Senhotenre would've chosen him as his successor. But there were no male heirs fit to rule at the time, which is why Narmer's father was chosen. That puts any potential boy around or younger than 20.
If this boy ends up existing, he and his family are very aware that he should never dream of becoming king under normal circumstances. Conspiring against the ruling dynasty is high treason, after all.
An official dynasty change happened with Senhotenre's death. Every surviving member of the old king's family has lost their right of succession. They have lost all titles, official functions, and the right to manage any assets owned by the crown and the state. Narmer's father allowed them to keep their private wealth, so they still live in relative luxury, but they lead a secluded, private life, out of the public eye.
I imagine, this boy would be there at the end of the line of succession though, just in case, but every single male member of Narmer's extended family would be ahead of him, and even some of the girls.
It's also important to note that the dynasty change did not happen by a coup or any violent means. Putting Narmer’s father on the throne was a collective agreement between Senhotenre’s close family and the highest members of government. The old royal family holds no grudges against Narmer's family for that. Essentially, they were the ones who put them on the throne. In fact, many of them quite like Narmer, both as a person and as a king. They would not get caught conspiring against him of their own free will.
