Complex sentence: Realizing their foolishness, Sethu and Unni patches up and reaches back home happily, when Sethu gets a letter from his father informing the arrival of daughter of one of his friend in Chennai.
Split into simpler sentences: Realizing their foolishness, Sethu and Unni patches up and reaches back home happily. But at home, Sethu gets a letter from his father informing the arrival of daughter of one of his friend in Chennai.