I have some information that I hope will help you in your search.
George Gallaher, David and Lydia's eldest son, was born at what is now Belleview, Missouri in 1805.He grew up there on his father's pioneer farm.In the late 1820's he went to the Middle Fork of the Black River between Edge Hill and Black, Missouri.Black was part of Washington County at the time but is now in Reynolds County.
Goerge married Serena Miner.Serena's father, Henry was a neighbor of George's and had come from Bolin Green, Warren County Kentucky.
Geroge and Serena's children: Josephine born 1834 married Mathew Adams Sarah married John Buford Martha married Albert Hendricks
Margaret married Monroe Fitzpatrick (Is this Margaret your Margaret?)
Milton married 1)___________ Black 2)Drusilla Goggin Louis did not marry. Catherine married Charles Hodges John married Charolotte Mallow Frand married 1)___________________ 2)______________ Goggin.
Eliza married Samuel Trollinger (Eliza and Samuel are my ancestors).
I may be able to get more information on Margaret and Monroe through family contacts.If I do I will pass it on to you.