Spotted this in the Notebook in Marown Wills. It mentions William Cubbon h/o Cath. This will be the elder couple with those names:
1792 A 8 GELLING Ann widow,ballaling;son john,patrick,robt;dau kath,ann;philip corris h/o ann,wm cubbon h/o cath

This will be Ann FAYLE, widow of John Gelling of Ballig, whose MI was listed here by Donna on July 12 2008.
#309 St Runius Marown
Here repose the remains of JOHN GELLING of Ballig who departed this life January 30th 1784 aged 79 years
also ROBERT GELLING who was Schoolmaster of this parish forty years he died on the 28th of January 1815 aged 62 years
also of THOMAS GELLING Mason son of the above sd ROBERT who died the 2nd of July 1849 aged 68 years
also MARGARET wife of the above THOMAS GELLING who died July 28th 1856 aged 72 year

The sons of John Gelling and Ann Fayle are all on the IGI but I can't find either Cath or Ann, nor the marriages.

Regarding the second couple who married 1781, I'm quite sure the Catharine will be the one b 1754 d of John Gelling & Cath Killey of Ballamillaghyn Braddan. She is mentioned as "Catherine Cubbon" as one of the many exec's on one of the attachments dated Nov 1812 of her parents' will (which conveniently is after the other Cath Cubbon's 1811 MI that Donna provided.) My theory is that she is a widow because in all other cases of married women the husband's name is provided.

I think this will be her husband, from the Notebook:
1793 A 15 CUBBON William dated 4 aug 1790;butcher;ch cath,wm;wife pregnant ? exex;1803: saml hill h/o cath

Samuel Hill md Catharine Cubbon 11 Aug 1801 Braddan. Catharine died in 1809.

In 1841 there is a 90 year old Catherine Cubbon living at Castletown. There's also a burial on Brian's index for "Cubbon ....." age 90 Braddan 5 Apr 1843. I wonder is this is Catherine Gelling b 1754?