The IGI indicates John Fea and Mary Alexander had at least two sons:
It is not known what became of Cornelius Fea. John Fea could possibly be the lock keeper in Falkirk who died in 1862. However, there are a number of points both for and against this and it is likely to remain conjecture.
There certainly was a John Fea who was a seaman at around this time. Anthony Farrington's Catalogue of East India Company Ships' Journals and Logs 1600-1834 (London: British Library, 1999) lists a John Fea (c 1747): seaman HMS Cormorant 6m; seaman Diana to Tenerife, 9m; seaman Vansittart (2) 1763/4; midshipman Hampshire (2) 1765/6; midshipman ASIA (2) 1767/8; 4th mate Greenwich (2) 1769/70; 3rd mate Greenwich (s) 1771/2 (approved 18 Oct 1771, aged 24); mate and master in country trade 3y; 1st mate Contractor 1779/80.
Further conjecture could be made in respect of the parents of John Fea who married Mary Alexander. There is certainly likely to be an Orkney connection due to the strong ties between Orkney and Leith. A possibility is the son of Mitchel Fea who was born in Stronsay in 1747. It should be noted that this is the probably year of birth of the seaman above although there is no verifiable evidence that he is the John Fea to marry Mary Alexander.
There could have been other John Feas born in the area around this time. It is noted that John Fea, the manager to John Fea VII of Clestrain at Stove in Sanday, had a son James in 1745 and a daughter Mary in 1759. It is always possible that he also had a son, named after himself, who does not appear on the Old Parish Records. This would give some more credence to the obituary of the lock keeper being a great grandson of John Fea VII of Clestrain. The parents of the manger at Stove are not known. John Fea VII of Clestrain did despone, shortly before his death on 29th August 1760, the farm of Seatter in Sanday to his namesake, the manager at Stove.