THe thing I find funny about this is that many of the "STEM legends" such as von Neumann, Ulam, Einstein and others had read a lot of classical literature. Einstein himself is quoted saying: "Dostoevsky gives me more than any scientist, more than Gauss." I just make sure I give this quote only when there are no number theorists in the room.
Sure, if one just confines oneself to the "popular" works on a standard YA list, it may be reasonable to conclude that some fiction is not worth reading for a STEM person. However, the classics are classics for a reason after all.
Moreover, it is also not implausible that a discerning eye can find plenty of great worth in modern authors as well, something the parent has done.
Edit: he may manage to become not a moron in the future, I just mean that I would proceed under the assumption that he is at this time a moron.
'My Struggle' by knausgard. Lengthy but worth it, even if you only read book 1. On face it's just the angst of some middle class writer, but following him into the recesses of his own introspection is really something.
The borderlands trilogy, Cormac McCarthy. This guy tackles major existential questions in his fairly simple (but dark) stories. it'd help to have basic grasp of Spanish for these books
And maybe my favorite book, Lullabies for little criminals by Heather O'Neill. It's about a little girl who's being raised by a junky and is coerced into prostitution. Obviously a very dark premise, but the way the protagonist experiences it made me think a lot about resilience, relative hardship,etc.