I have traced your and your late cousin Brian's family tree back to a George Fordyce of Monquhitter, Aberdeenshire whose children were being baptised there in the 1760's and 1770's.
Please contact me for further information. Your father Benjamin Sydney Fordyce (1910-1980) was the son of Benjamin Fordyce(Ben)(1877-1939) and Isabella Bainbridge Reid(Bella)(1880-1954). Benjamin Fordyce was one of 7 children of John Mackie Fordyce(1849-1888) and Margaret Millar (1852-1903). John Mackie Fordyce was one of 11 children of James Fordyce(1805-1880) and Jean Mackie (1810-1853).James Fordyce had a further 7 children by his second wife Christina Patterson (1829-1878).
James Fordyce(1805-1880) was the son of a George Fordyce (1769-?1848) and Christine Clarke and George Fordyce himself seems to have been one of the 8 children of another George Fordyce by an as yet unknown wife.
I also have some details of the Millars and Reids if they are of interest. The Bainbridges have been a bit more elusive to track down.