Complex sentence: Xiahou Xuan's mother was Cao Shuang's aunt (the sister of Cao Shuang's father), and he was close to Cao Shuang's faction but survived the overthrow and execution of Shuang and his faction in 249.
Split into simpler sentences: Xiahou Xuan's mother was Cao Shuang's aunt (the sister of Cao Shuang's father), and thus he was close to Cao Shuang's faction. Despite this, he survived the overthrow and execution of Cao Shuang and his faction in 249.