The case of how exactly Aleksander managed to get away with the Darklings being always a father and a son is absolutely underexplained, and even the books themsleves acknowledge on how thin of a thread the lie was holding on.
No king ever demanded to meet the current Darkling's son under a threat of some serious consequences?
No one ever tried to investigate where the Darkling's family lives, who it consists of, who are the children raised by, and what are they doing before the son comes to take up his father's position?
Darklings were arriving to Os Alta already fully pepared and trained, which means, they had Grisha teachers in that house wherever it was, which means, there is a possibility of a whole another group of strong, educated Grisha living Saints-know-where, under Saints-know-whose supervision. If that doesn't look like a threat to the Crown, I don't know what does.
Especially that is's very hard to believe the Darkling's... hard to say wife, but just a mother to his child, will always have one kid, and it will always be a son. No one ever started question the probability of it all? Never started to ivestigate it? Or someone has, but found nothing? But then that's even more suspicious. How were the Darklings not eradicated yet?
