I do not know the names of Archibald Meharg's parents. I'm descended from James Downing via his second wife, Mary Clark, but I know this Archibald Meharg served in the Revolution, was probably married to a Rebecca (with a maiden name of POSSIBLY Bolt... or not). And I've seen mentions on the internet that Archibald Meharg may have married Temperance Coker (another Laurens County resident) in Alabama (I have no evidence of this, though). He died in St Clair County, Alabama. (The Cokers also ended up in Benton/Calhoun County, Alabama, and their family is always there alongside the Downings and Mehargs.)
The children of Mary Meharg and James Downing were: Archibald, Susan, Thomas Jefferson, Jencie, and Mary (who may have also been called Mary Ann or Polly). All these children appear to have been born in South Carolina or Tennessee. The 1820 Alabama Census confirms 2 boys and 3 girls, all still under the age of 21 (this census disguishes between those over or under 21). There is no other female in the house, indicating Mary Meharg had died by then. James remarried a couple years after that, and had 11 more children by his second wife.