Oh mate, that's the least messed-up thing here, therefore the author is undoubtedly correct. I don't know what planet you reside on, but I can assure you that people still marry cousins today on earth(I've seen them)..
~ Please say goodbye to the IF and yourself if the story doesn't meet your expectations.
You have the audacity to criticize the author for crafting the tale in their own distinctive way. Which is quite awful and.....You need to develop the ability to criticize someone while remaining polite.