and if we fantasize a little about the future, then I would persuade Zara to put one of her sons in a book with erotic stories with incest and see "how the pendulum of history swings", because it seems that Zara has a kink for incest, doesn't it? Well, you need to cheer her up. she's just afraid to be the first to approach her son. Well, let the son take the initiative.
and even if nothing comes of the idea of real incest with one of her sons - she still has the backup option of role-playing with the MC as an "alternate airfield" - what does Zara lose?
surely Zara has one of the sons - dependent and preoccupied with sex. such a person hardly has any independent future - so if mommy takes him to her bed - nothing bad will happen from this for world development. on the contrary, the son and mother will be more satisfied with life - there will be more for two happy people in the world - why not profit?
so at the next "review session in the archive room" the MC could start slowly putting smart thoughts into Zara's head, especially when Zara is close to the finish line. =)