Uncertainties regarding the age of the lock keeper when he died in 1862 and consequently when he was born, together with incomplete or possibly incorrect information on the death register, also create uncertainty with regard to his parents and further back generations.
The Falkirk Herald obituary states that John Fea was a great grandson of John of Clestrain. John Fea VII of Clestrain never married but had two illegitimate children, Henry and Alexander Fea, in 1747. Henry died in 1762 and no record has been found of Alexander after 1774. If the lock keeper was born sometime between 1767 and 1791 but possibly around 1777 (based on his age on the muster list of the Indefatigable in 1804) then there is not that great a time period for the intervening generations.
If the year of birth derived from the obituary is taken, then 1767 is the earliest of the possible years. The Fea surname is not common. It is noted that a John Fea was born to John Fea and Mary Alexander in that year. There are points both for and against them as his parents and it is likely to remain conjecture.