Complex sentence: He further explains that under Klingon tradition and law the family of a Klingon warrior is held accountable for his acts, as the warrior is for theirs; if he fails in his challenge he and Kurn will be executed.
Split into simpler sentences: He further explains that under Klingon tradition and law the family of a Klingon warrior is held accountable for his acts, as the warrior is for theirs. He adds that if he fails in his challenge he and Kurn will be executed.