As a Gelling researcher, I know a bit about the family of Mary Gelling who married Thomas Cain 12 Sep 1804 Braddan. She was bp 30 Nov 1783 Marown, d/o Robert Gelling & Jane Kelly, miller of Ballagraw, and gd/o John Gelling & Catharine Killey of Ballamillaghyn, Braddan (much discussed in this forum in the past).
Thomas Cain & Margaret (Gelling) moved to Liverpool about the time of son John's birth (1810ish). Thomas was a tailor living on Cunliffe Street when he died age 39 in 1819. Their son John age 30 is at Croston Court, Cunliffe Street, Liverpool in 1841 with his younger brother Joseph. Also there in the same house is William Clegg age 20 bricklayer who is an ancestor of JeanC and Kay Clegg regular contributors to the board. In 1851 John Cain is at 30 Duke Street Liverpool age 41 married, barber and hairdresser b Liverpool, but he is alone. I can't find him after that but the common name makes it difficult. Could this be the John Cain who married Esther Hampton, widow, 27 Feb 1838 Braddan? If so, he's not with her in either census. I haven't looked for Esther.
The widow of Thomas Cain, Margaret Gelling, then married her cousin John Gelling (s/o Wm, brother of Robt) 4 Jan 1829 at St. John Liverpool. John Gelling died 30 May 1838 at Croston Court, Cunliffe Street age 43 and the informant was Joseph Cain. I don't have Mary's death but likely before 1841.
I have nothing for the parentage of the Thomas Cain who married Mary Gelling.