but it's very typical in an abusive/dysfunctional family. I was on a website (long since taken down) where people discussed having abusive parents (generally narcissistic or sociopathic parents) and it's very typical for at least one child to be the 'golden child' and one child to be the 'scapegoat'. Sometimes there are more than one of each. In my family, I was the scapegoat and my brother was the golden child, although he actually got beat more, he was also the one that my parents lavished attention (and money) on. I was good at making myself invisible to avoid the beatings and so managed to make myself completely invisible to my parents, except if they needed me to do something. The dynamic exists to this day, even though my brother and I are both in our late 30's.
The same thing happened with my dad and his mother. He had 2 sisters (they were born 15 years apart, with my dad in the middle) who were absolutely adored and treasured. My dad was reviled. His sisters received gifts at Christmas while he received coal (no joke, that actually happened). His mother nitpicked him nearly to death. She made him do all the housework. She beat him if it wasn't good enough. My grandfather tried to stay out of it (he was never abusive, never laid a hand on my dad ever, and tried his best to protect my dad by taking him everywhere, but that would make my grandmother even more furious. They divorced when I was 4 years old). Even as an adult, she picked on my dad. She confided in me when I went through my divorce about how much she hated men (and in particular my grandfather, which was uncomfortable, since I adored him). So I gathered my dad got the short end of the stick because he reminded my grandmother of my grandfather. There are 4 grandchildren in total, and guess who is the favorite? Me, because I'm the only girl. Long story short, I don't talk to her anymore because of some horrendous things she did after my grandfather died.
But yeah, typical dynamic. I'm not sure what the abusers get out of it, other than leverage to play one kid against the other. It's creepy to me.