Thomas's parents might be John Gelling and Margaret Caroon who married 1767 Braddan. There is no IGI entry for Thomas, but he is the executor for his father's 1822 will (John Gelling Sr of Ballacaine Braddan). I can't find any other Thomas who comes close to matching.

The Thomas who is the father of Desley's ancestor Edward was 82 at Ballanicolas Marown in 1851, farmer of 70 acres, born Braddan. The math works out to 1769 so it's in the range.

The above JG who died 1822 was bp 4 Oct 1741 Marown s/o John Gelling & Ann Fayle of Ballig, . Their son Robert was the Schoolmaster of Marown.

A fabourite conjecture of mine is that the JG (b abt 1705 and died 1784 age 79) who married Ann Fayle about 1732 could be the son of John Gelling of Ballamillaghyn by Ann Kneale, executor of his father John's 1733 will. This would be the younger son named John. The elder son John inherited Ballamillaghyn Braddan but he died 3 years later and passed it to his teenage son John who held it for 75 years until he died 1812 age 90.