According to Royal naval biography, or, Memoirs of the services of all the flag-officers … by John Marshall, Lieutenant Charles Hope Watson, Esq married in July 1824 Mary, youngest daughter of the late William Ramsay, of Barnton, co. Mid-Lothian, ‘Esq. He was the third son of the late Charles Watson, of Saugkton, co. Mid-Lothain, Esq. by Lady Margaret Carnegie, sister to Admiral the Earl of Northesk.
I found marriage of Charles Watson and Margaret Carnegie in Debrett’s Peerage of England, Scotland, and Ireland by John Debrett . It also shows that Charles Watson, of saughton was third son of of James Watson, of Saughton, co. Edinburgh, esq and Helen, daughter of Charles, 1st earl of Hopetoun.