I disagree that a mother’s job ends when their child reaches the age of 18.
While my mother didn’t completely cut off contact with me, she did kick me out. I was forced to live many miles away where I knew no one. And this was very hurtful and, I feel, a selfish decision on her part. I would never do that to any child of mine. I wasn’t even a “horrible person”
The parents didn’t have any formal mental health diagnosis. Step maternal unit I would say has sociopathic tendencies if not the full disorder