Robert Barclay, Esq.

According to https://archive.org/stream/genealogicalacco1812barc/genealogicalacc... - "A genealogical account of the Barclays of Urie" which was written about the year 1740, by Robert Barclay (1672-1747), the son of the Apologist, the said Robert Barclay only had one wife Elizabeth Brain by whom he had two sons, Robert and David, and three daughters, Mollison (who married John Doubleday), Elizabeth (who married Sir William Ogilvie), and Catharine. He never went to America so could not have married Margaret Kerr - while she might well have married a Robert Barclay, it could not have been the son of The Apologist - and the children attributed to Margaret Kerr were not his.

More Information on link below:

://books.google.com/booksid=kjme027UeagC&pg=PA159&dq=Gilbert+Molleson+of+Urie,+Kincardine,+Scotland&hl=en&sa=X&ved=0ahUKEwj1I_lwIPaAhXIulMKHYovDDkQ6AEILzAB#v=onepage&q=Gilbert%20Molleson%20of%20Urie%2C%20Kincardine%2C%20Scotland&

Geni Profile above I found Robert Barclay of Urie married 2x, Elisabeth Brain & Margaret Kerr the mother of Margaret Kerr King (Barclay)