Rachel,
The Niven side of my family is descended from Thomas Niven (b. 24 April 1803, Barefoot of Forteviot; d. 17 August 1877, Woodend, Madderty), who was William's brother. I have a tiny bit of info on the other siblings but have not yet explored the Edward side of the family.
Laird Niven
Dartmouth, Nova Scotia, Canada