Rob, just to clarify things for your many readers here, can I be pedantic and say that your grandfather was James Flett Horsburgh, not just James Flett.
I used to correspond with and visit a relative of Ellen's in my home town of Cellardyke who was a distant cousin of mine and who was interested in her family history, and although her (our!) Cellardyke and Pittenweem ancestors were easy enough to research, we struggled with the Fletts, trying to work out who was from Portknockie and who from neighbouring Findochty. Robert Horsburgh and Mary Flett were married in Findochty, but in the later censuses Mary claimed to have been born in Portknockie.
I was told that after Mary Flett moved to Pittenweem, she sang its praises to her family back home, so they packed all their worldly goods into their boat and moved to P'weem. There are still descendants of the Fletts living locally. My sister's late mother-in-law in Pittenweem was one.
One interesting thing about the P'weem Horsburghs is the incidence of multiple births, not just twins but several sets of triplets, long before the days of fertility treatment. Robert Horsburgh and Mary Flett's son George Horsburgh (b.1864) was grandfather of the Lindsay triplets who started and finished at St. Andrews University on the same day. I think they all became science teachers. Two of them, Beatrice and Preston, taught at my old school, the Waid Academy in Anstruther. While I was there Beatrice married my Latin teacher, and Preston was my biology teacher in 2nd year.
Harry