I'm seeing the money issue as something concrete that the LW can explain without getting into a lot of emotional pain that people might want to debate them about -- whereas the emotional and financial neglect in childhood. *The LW says it's a lifelong pattern.*

This isn't solely about the money.

"They accuse me of loving my in-laws more than them."

The parents are engaging in emotional blackmail, to start with. And they have a history.

They want the LW and their husband to bring the kids TO THEM. The parents are not exactly coming off smelling like roses, frankly.