Like KathleenGrace wrote, N's mother manipulated the thinking of everyone in the family. She enjoyed nothing more than pitting family members against one another, but if you tried to point out what was really happening, they turned on you like pack of jackals - they were completely unwilling to admit that their mother would set them up, even though all of her children hated her to one degree or another.
It was a very messed up family.
Her husband was fairly useless too - I'm not entirely sure what his actual problem was, but he was always angry about something (usually caused by his crazy wife) treated everyone in the family with undisguised contempt. He fought with N's mother constantly, but more or less didn't bother defending his children against her craziness. To be fair, I didn't know him until all of the family was grown up - maybe he did defend them at one time, but I doubt it. He basically absented himself as much as possible when I knew him.
Like KathleenGrace said as well, if you asked one of the combatants why they were fighting, it would be their mother's words that came out of their mouth. If you asked further questions about the logic of it, they would just get exasperated and refuse to answer your questions.
In that family there is N, his sister who is probably a Manic Depressive, another N, an H younger sister and his younger brother who didn't appear to have a personality disorder but became an alcoholic.
Some legacy to pass on, huh?