My NPD mother spent our entire childhood running down our father constantly. The worst insult she could throw at us if we displeased her was, "you're just like your father". My brother recently told me he was ashamed of becoming a man when he hit his teens as Mum was constantly going on about men being awful.
She would have tantrums and rows every time Dad was at home and throw stuff at him - cups of hot tea, a portable television. We all lived in fear of her rages.
She divorced my Dad when the youngest of us kids hit 16. In fact, she spent our whole childhood telling us she was just staying for us until the youngest hit 16. Way to pile the guilt on us, Mum! 
There was nothing wrong with my father. He ran a business that he spent more time at than he perhaps should have, but as he told me many years later when he was dying, he felt there were fewer rows when he was out and that it wasn't good for us kids to be around those rows. That was true - she was better when my father wasn't around to vent her spleen at. As kids, we didn't get too close to him when he was around as Mum would get jealous and we'd pay for it later.
She never had any cold hard facts about what was so awful about him, but she had a habit of falling out with her own family and not talking to them for decades over nothing anyway. Meanwhile, my father never said one negative word to us as children or adults about our mother.
35 years post-divorce and Mum is still the same. She has guilted another family member into sharing a house with her and that family member's mental health has gone right down and I am quite worried about them, in fact.
So to answer the OP, despite years of indoctrination, we all realised the other parent was not the awful person they'd been made out to be.