According to Mason Co KY marriage records it shows Thomas PURNELL marrying Elizabeth HICKMAN on 20 JUN 1849 with bondsman as Charles B. SMITH.
ALSO note that it seems that the other brother is William PURNELL in the Mason KY 1840 census.William married Caroline CAHILL in Mason Co KY on 06 AUG 1842 and the application showing the bondsman as George W. SOWARD on 01 AUG 1842.
The other brother, Armstead, married Julia OUTTEN on 05 FEB 1838 and the application showing the bondsman as Jacob OUTTEN, Jr. on the same date.
It appears that the brothers were born in the following order: Armistead, William, and Thomas.Apparently all were born in VA.Be wary that there may be other brothers as well.
Evidently this group has ties to possible Revolutionary Soldier in VA.Considering the timeline this family may have served with George Rogers CLARKE on his many expeditions protecting KY against Indians and British forces.
Check into the land patents to see if there is evidence of military or militia service writs being honored and the lands being proved by the sons.
Look at the land records to check the deed descriptions and see who are the neighbors on the boundaries which may prove to be relatives.
Sometimes when you look at the land records you will find that there may be some relatives involved in the surveys of the lands before they became relatives.
Something else to consider is that each time a county is formed they usually take a census to find who is within the new boundaries.
Remember that our ancestors left a paper trail.All of them.We family genealogists just have to look in the right place for that paper trail.