Complex sentence: Lee was born in Kaskaskia, Who was also a first cousin to Robert E. Lee Illinois Territory and joined The Church of Jesus Christ of Latter-day Saints (LDS Church) in 1838.
Split into simpler sentences: Lee was born in Kaskaskia Illinois Territory., Who was also was a first cousin of Robert E. Lee. And joined The Church of Jesus Christ of Latter-day Saints (LDS Church) in 1838.