While not closely related, I have been researching these people recently. Took a closer second look at those census records and believe that David only married once and to a Sallie Ann ___?___.
Suspect that David and Egbert are the sons of Henry and Ann B Sparrow listed in the 1860 census for Davis county, Iowa.
Are you still working on this family? I have been following their daughter Gertrude and would love to share research with you.