A couple of the Michigan marriage records for his children also have him born in Tennessee as do the 1880 and 1870 censuses (see familysearch.org).
Going by the 1850 census of Mercer Co., OH it shows the oldest children Richard and Denis born in PA while George, Mary,and Mariah were born in Ia which does not mean they were born in Iowa. Standardization of two letter abbreviations for states did not state until the 1970's. If you look at the Indiana censuses from the 1850's and 1860's you will find tons of people born in Ia. I guarantee you there wasn't a massive shift of people moving from Iowa to Indiana. In other words back then Ia stood for Indiana as easily as it did Iowa. Also it looks like the last children were born in Ohio after going to Indiana (or Iowa) rather than before.
After that it is very hard to find any of the family members. It could be they all moved on or several of them had died young.
The best I can suggest is to get David's obituary. With any luck it may have surviving siblings and exactly he was born. I would also track down as many of the siblings as possible and get their obits, death certificates and marriage records. The chances are good that at least one of them has Sally's maiden name. One of them might also have where Christopher and Sally were born. In other words looking for info on a sibling can lead you to what you are looking for.