My great-great-grandfather is Thomas Vern Maxwell (b. 1826, Ohio; d. 1916, Iowa). Sources differ on his parentage, however. All indicate his mother to be a Sarah Conover, but differ on his father. Some show the father to be John Warren Maxwell; others say he is John B. Maxwell. The listed parentage of each of these "Johns" differs. So which John was Sarah's husband, and how do we know for sure?