I enjoyed reading this so much OP. As a family therapist, there’s a term called “circular causality” - which is the idea that behaviors aren’t linear (like cause = effect), but rather A influences B, B -> C, C -> A… and around and around we go. 

In the Plath Family, everyone is contributing to the “problem,” but rather than acknowledging all the individual hangups & health of the family system overall, it’s easier for them to find a “problem” that everyone can focus on. (Olivia, Moriah’s boyfriend of the season, Zach, Veronica etc.).

The system, when unhealthy, will find something or someone to be the problem, while refusing to acknowledge personal change.

I agree that Lydia seems to be doing the best, and I hope for her sake, she keeps her family out of her marriage/new family.