So, it just occured to me that Gregor Clegane doesn’t appear to have a wife or family. Although I’m really glad that for that(as a human being with empathy and feelings), isn’t it a huge dereliction of his duty as the head of a house? Shouldn’t that be addressed in the narrative?

Actually this has been addressed in the text:

Ned Stark could not recall ever speaking to the man, though Gregor had ridden with them during Balon Greyjoy’s rebellion, one knight among thousands. He watched him with disquiet. Ned seldom put much stock in gossip, but the things said of Ser Gregor were more than ominous. He was soon to be married for the third time, and one heard dark whisperings about the deaths of his first two wives. It was said that his keep was a grim place where servants disappeared unaccountably and even the dogs were afraid to enter the hall. And there had been a sister who had died young under queer circumstances, and the fire that had disfigured his brother, and the hunting accident that had killed their father. Gregor had inherited the keep, the gold, and the family estates. His younger brother Sandor had left the same day to take service with the Lannisters as a sworn sword, and it was said that he had never returned, not even to visit. (Eddard VII AGOT)

Gregor murdered most of his family and all of his wives.