Complex sentence: Atreus broke a promise to Artemis, who in turn cursed his family--a house descended from Pelops and Tantalus, who fed his own son to the gods at a dinner party.
Split into simpler sentences: Atreus broke a promise to Artemis, who in turn cursed his family. If that wasn't enough, the house was descended from Pelops and Tantalus, who fed his own son to the gods at a dinner party.