How we cite our quotes:
Quote #1
She called her dad instead. He sounded tired, but he wasn't trying to replace the stairs with a water slide, so that was an improvement. (6.159)
Cath's dad has bipolar disorder, which means he alternates between depressed and manic. Mania in a nutshell: trying to replace the stairs with a water slide.
Quote #2
"I remember thinking that me and Abel would never be like Dad and Mom, that if Abel ever got tired of me, I'd survive it." (7.79)
There's an old cliché that we date and/or marry our parents. (People like them, that is—marrying your actual parents is all kinds of wrong.) In Cath's case, she chooses a safe boyfriend who's her parents' complete opposite.
Quote #3
They had the same DNA. The same nature, the same nurture. All the differences between them didn't make sense. (8.65)
Wren and Cath may look identical, but they've never had identical personalities. Wren's the extrovert, Cath's the introvert, and college brings out their differences even more.