I feel like I was very easily able to recognize this when my brother was catching a lot of flak from my parents for struggling in school (this was several years ago, when I was still in high school). I was very angry at them, I did my best to comfort my brother and stand up for him as much as possible. But eventually, my brother's relationship with my parents improved to the point where now he is their favorite child, and mine continued to deteriorate until I've basically become the family pariah. The thing that I get kind of sad about is that my brother in turn doesn't really try to understand or comfort me at all. I get that he probably doesn't want to stick out his neck for me, but he defends my parents to me even when they aren't listening. I feel like in the past we had more solidarity as siblings, and now it's completely gone.

There's definitely some enmeshment going on here. I was skimming through a book yesterday that talked about how in family dynamics where there's a preferred child, usually it's because that child is on a more similar plane of emotional maturity to the parent (don't know if I agree with the framing of "maturity" exactly but it's what the book uses.) My brother is definitely less outspoken, less visibly mentally ill, and honestly, much less of a leftist which I think is a part of it (he's vaguely "apolitical" but in the way that a lot of teenage boys are, I've caught him saying slurs in Heated Gaming Moments™ before.)