Heavy Snow in Taiyuan, Chang'anxia

From the cold winter in Taiyuan City in the 13th year of Daye to the hot summer in the 9th year of Wude. The four fathers and sons, Li Yuan, Li Jiancheng, Li Shimin, and Li Yuan, moved towards an uprising against the Sui Dynasty after the Liu Wenjing incident. They also gradually moved towards mutual suspicion and murder among relatives. They also experienced Yang Wenqian's rebellion. The conflict between the three brothers reached its peak. Why did Li Shimin go to the Xuanwu Sect to kill his brothers, and what did Li Yuan do?