Complex sentence: The White Face Barghast join as well after Trotts proves himself in single combat against the key chief's son, whose other children discover that the Barghast are descended from T'lan Imass who didn't bind themselves to the Ritual of Tellann.
Split into simpler sentences: The White Face Barghast join as well after Trotts proves himself in single combat against a key chief's son. The chief's other children discover that the Barghast are descended from T'lan Imass who didn't bind themselves to the Ritual of Tellann.