I also find it interesting that Carrie's untreated bipolar disorder is coupled with some major gaslighting ("Nooo, we had NOTHING to do with that newspaper story"), so it's a double-whammy to her sanity. Also - and I admit that I might be stretching this a bit - the misogynistic double-edged sword of "women being too…
Harrison is even more than a step-sibling to Astor & Cody. He's their half-brother, since Rita's their shared mom - which makes this even more egregious. They're the only people who could have really told him about his mother from the perspective of her offspring.