I am pretty sure that when my DH and I got together, because we were both escaping family traumas and upsets, we parented each other. We were equally the stable mother and father we needed and the children who finally got a chance to blossom and play. He was the kind father I hadn't had and I was a substitute for his overstrong (and somewhat bonkers) mother.
After ten years of mutual therapy we were ready to have the DC we produced who grew up a bit saner than we were. But only a bit because, of course, we passed some of the behaviours down the line. We hope we only passed the fun bits on and the DC tell us they had a great childhood.
In my own family, I am my DS's scapegoat. Whenever she's stressed or her DH or DC upset her she lets loose at me. She has no idea she's doing it as she has the self awareness of a grapefruit.
Family fun and games!