He was s of Maj-Gen Cecil Llewellyn FIRBANK CBE DSO 1903-85 and his 1st w Audrey 1912-2004 d of Sir Reginald Arthur HOBHOUSE 5th Bt 1878-1947 and Marjorie Chisholm 1877-1967 d of Frederick SPENCER 1837-1918 by his 30 April 1874 m to Jamesina Chisholm MACPHERSON 1842-1906. He m 1962 Caroline Anne d of Major J T C HOWARD of Tregatreath, Coverack, Cornwall, and had two sons and a dau as above.
I have sought to identify "Major J T C Howard", and I have come to the conclusion that he was Lt-Col John Thurstan Collins HOWARD, MC (4 XII 1919 - 30 XII 1998), who was a great-grandson of the Very Rev and Hon Henry Edward John HOWARD (14 XII 1795 - 8 X 1868), the youngest son of the 5th Earl of Carlisle.
Lt-Col Howard's wife (married 2 X 1949, as her second husband) was Margaret Elphinstone Flamank EDYVEAN (11 XI 1916 - 13 III 1979). Her first husband (marriage registered Q1 1942 - Kerrier) was Marcus J MITCHELL, whom I have tentatively identified as Marcus James MITCHELL (2 II 1915 - 9 IV 1990).
It appears that the late Mr Firbank's first wife, Caroline Anne HOWARD (1942 - 4 VII 2007), was born as Caroline Anne MITCHELL (birth registered Q1 1943 - Redruth, mother's maiden name Edyvean), and that she was therefore Lt-Col Howard's stepdaughter, rather than his daughter, despite the fact that their gravestone does not make his distinction (see https://www.findagrave.com/memorial/257011026/caroline-anne-firbank).
The late Mr Firbank's widow, nee Rosemary Rachel DEAS (born 12 VI 1936), whom he married in 1989 as his second wife, was previously the wife (married 29 VII 1956, divorced 1987) of Sir Peter George Culcheth HOLCROFT, 3rd Bt (29 IV 1931 - 26 X 2009), and is herself a 4 x greats granddaughter of the 1st Earl of Uxbridge, father of the 1st Marquess of Anglesey.
Margaret Elphinstone Flamank EDYVEAN was the daughter of Robert Courtenay Flamank EDYVEAN (1885 - 23 VII 1958) and his wife (married 1914), Ella Maude Murdoch MUNRO (28 X 1889 - 30 IV 1970). Robert Courtenay Flamank EDYVEAN was the son of Bernard Flamank EDYVEAN (30 IX 1850 - 17 VII 1928) and his wife (married 29 III 1883), Elizabeth Elphinstone CLACK (20 II 1862 - 9 VI 1939), of that family, formerly of Crowmarsh Gifford and Larkbeare, which, per Burke's Family Index, last appeared in Burke's Landed Gentry in the 1937 edition.