Oh, so now I'm to investigate Smiths in Liverpool? What have I ever done to you!?
And I'm struggling to find where I mentioned Smiths in Liverpool ...
(Remember, "Smith" in my own case was just a stand-in invented for the actual supposed surname, which was only one step less common than that.)
Could be interesting, at least they aren't John and Mary.
Fernley was a briefly popular name for Smiths 1890-1920ish -- 14 of them, almost all in Plymouth / Devonport / East Stonehouse (Norfolk for the others). So your Smiths do seem like transplants.
Any idea of the timing of those letters?
Most of the Fernleys died in childhood though.
1892-1893
1894-1898
1895-1896 (Norfolk)
1902-1902
1911-1911
1907-1912 (he is the one in the 1911 census)
1915-1915
that leaves
Fernley H 1909 Blything married 1940 Surrey SW, I don't see a death
Fernley R 1922 Devonport married 1950 Middlesex, died 1999 Dorset
Fernley 1922 Devonport, died 1983 Plymouth
and births in Plymouth in 1951 and 1955; both married in the same area.
Looking for siblings would be monumental; even with unusual surnames, we're still looking at Smith.
but o m g, I tried the most unusual surname and lo, there is a brother Cyril, 1919 Devonport, for the 1922 Fernley who died in 1999. Cyril Claude Smith died 1986 Plymouth. There look to have been others elsewhere with the same surnames ... amazing, with a name like Wilbraham, there are 15 marriages to Smith after 1916 even. But here is ours:
Fanny C Wilbraham + Reginald C Smith, 1914 Devonport.
Except you said Florence. Could she have been one of those modern young women who tarted up her name from the olde fashioned one she was given?