These are the rigid family roles that develop in dysfunctional families. This video by Jef Gazley relates to alcoholic family systems, which is often an issue for the parents or the adult children of a narcissist, or both. In my experience this is very helpful to understand and many of the same ideas also apply if the core issue is mental illness in a parent too.
There is a dysfunction, such as addiction or mental illness of the parent that requires these roles to form. The parent is not functioning as parent in meeting the needs of the children in a healthy way. Inside the children are often angry, insecure and do not feel good enough.
Inverted parenting is a hallmark of an alcoholic family, as well as in a family with a narcissistic personality disordered mother. This situation causes post traumatic stress disorder. None of the children are getting their emotional needs met in a healthy way. Each position that the children fill serves a purpose for the family.
My brother had a heart of gold and deeply loved his family. He was the kind of man who would give you the shirt off of his back if you needed it. He was known for his heart of gold. It was his biggest asset. It may also have been his biggest downfall, second only to his own mother.
My late brother was taken from us only months after our narcissistic mother died. Their deaths stand in as stark of contrast as their hearts. She was completely self-centered, immature, manipulative and dishonest, but masqueraded as a selfless saint. He was known for his heart of gold, but ostracized and disrespected by his entire extended family of origins based on her slander.