Complex sentence: The Grand Prince SuYang attempts to build an alliance with his brother King MunJong's trusted prime Minister, Kim Jeong Soo's family by proposing a marriage between his eldest daughter SeRyung and Jeong Soo's son, Kim Seung Yoo.
Split into simpler sentences: The Grand Prince SuYang attempts to build an alliance with his brother King MunJong's trusted prime Minister, Kim Jeong Soo's family. He proposes a marriage between his eldest daughter SeRyung and Jeong Soo's son, Kim Seung Yoo.