 Martha's brother, George Robertson (1790–1874), studied law under McKee, succeeded McKee in the Congress (1817–1821), and served as Chief Justice of Kentucky (1829–1843 and 1870–1871).He also declined four cabinet offers and two Supreme Court nominations.McKee's brother-in-law was Robert Perkins Letcher (1788–1861) succeeded Robertson in the US Congress, and later served as the fifteenth Governor of Kentucky (1840–1844) and Ambassador to Mexico (1849–1852).