Mike - I have dug through some of Stephen's past. Haven't turned up anything on his in-laws yet. Yes, Stephen was born in Iowa and lived in Rock Island, Ill. until he joined the military. From records I have he also notes that he was married twice - can't find the first marriage but second was to Martha.
Martha's mother, Nancy J., married a Joseph Cossart in 1854. This was the second "Nancy" for Joseph. From notes given to me by my Mother, Joseph met Nancy while she was with child (Martha), and moved her to Arkadelphia where they married. Doesn't say where Nancy was when she met Joseph but only that her first husband died from the Mex-American War. That's why I think he was vet who either had a serious illness from the war or was wounded.
Nancy and Joseph stayed in Arkadelphia, AR, while Stephen and Martha ended up moving to Hot Springs area for the remained of their lives. 1860 census for Nancy and Joseph Cossart show Martha as a 6 year old, with a Cossart last name. 1870 Census shows Martha with Nancy and Joseph Cossart but with her biological fathers last name, Childers (the census says Childress but if you look at it closely it reads Childers). Martha uses Childers on her marriage license and all future Census with Martha list her saying her father was born in Alabama and mother (Nancy) in SC. Joe Cossart was born in Kentucky.
Got off on a tangent ---- sorry. Yes, if you find anything on Stephen P Moore's in laws that would be awesome...