Reddit reviews Campbell and Reece's Biology Eighth (8th) Edition (Hardcover) (Textbook Only)

A Tree Grows in Brooklyn - on reading and education as the door to escaping poverty. Might be a little young for them.

The Grapes of Wrath - on the humanity and the inhumanity humans and industry are capable of in harsh times. Might be a little long/dry/boring.

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Basically any science fiction novel by Greg Bear, because they are probably mind-blowing in vision to a teenager who hasn't had exposure to ideas of such scale (at least, they were to me. But I don't know how the parents would react to them, or if these girls like science fiction)

Blood Music- themes of nanotechnology and perception changing humanity

The Forge of God- on the destruction of earth once it becomes noticeable enough to aliens. And its sequel

Anvil of Stars- on whether revenge can be justified, how libertarian/cooperatives groups break down or are usurped, and an unusual alien race.

Queen of Angels- on psychology, consciousness, artificial intelligence, virtual reality and the beginnings of an internet (before there was an internet).

Eon- an asteroid suddenly appears in orbit, and its unusual history and construction destabilizes earth during the Cold War, but opens the door to alien technologies and civilizations. And its sequel

Eternity- the far future of humanity, conflict with an alien race, travel in space and time.

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But to be honest two books that would give them a fundamental understanding of how the world actually operates, if they aren't being exposed to it, would be:

Campbell and Reece's Biology

and

Chemistry: A Molecular Approach

They don't require too much math other than algebra, and though they're kind of expensive, they're worth it. The utter logic of how scientific thinking is done can be easily introduced with biology and an understanding of the atomic framework chemistry teaches is invaluable because it explains so many behaviors in our world. Maybe in e-book format or something, so they're not as obvious.