Meriwether Lewis (Corps of Discovery co-leader) is William Clark (Corps of Discovery co-leader)'s brother-in-law's first cousin's wife's brother!

William Clark (Corps of Discovery co-leader)
 

→

Elizabeth Anderson
his sister

→

Lt Col Richard Clough Anderson, Sr
her husband

→

Robert Anderson, III
his father

→

David Anderson, Sr.
his brother

→

Edmund Anderson
his son

→

Jane Anderson
his wife

→

Meriwether Lewis (Corps of Discovery co-leader)
her brother