Your Thomas still remains elusive. He's not the TG who married Eliz Hampton 1834, as that is a second marriage for a TG born ca 1790. This TG's first wife Elizabeth Kelly died 1832. You can find him with the second Elizabeth and children from the first marriage plus their own child Esther in 1841 in Douglas. Ancestry has indexed it as "JELLEY". He was a shoemaker and died in 1843 age 53. His widow went up to Poolyilley Lonan and died 1870. I can't figure out his parents at all, as there aren't any Thomas Gelling baptisms on the IGI for several years either side of 1790.

You also mentioned finding a TG & Elizabeth in the census's 1841-61. That's yet another elusive Thomas! This one married Elizabeth Craine in 1824 Braddan and had 8 children. Thomas died 1869 and Elizabeth 1874, so that's why they aren't in 1881 census. His ages in the census and burial work back to 1799-1801. I figure he's one of these:

1. son of William Gelling & Margaret Kneen bp 25 Jan 1801 St. Geo Douglas
2. son of John Gelling & Isabella Cavendish bp 11 Aug 1799 Braddan.
3. son of Thomas Gelling & Elizabeth Kelley bp 27 Jun 1802 Braddan.

My preference is #2, which would make him "your Thomas". The ages match best, and his census birthplace was Braddan, not Douglas. However, I'd like to find homes for the other two.

The erratic ages in the census's, particulary for wife Elizabeth, isn't unusual. Actually only 1851 is out of whack; the other point to about 1796 Braddan for her. I have a note that perhaps she is the daughter of John Craine & Anne Caine, bp 21 Aug 1796 Braddan.

The grandchild Margaret A. Cottier age 7 in 1861 and 17 in 1871 (with widowed Mother at Old Road, Patrick), born Liverpool, is a mystery person. Perhaps one of the daughters had a child? Daughter Isabella was buried 1854 in Braddan. I haven't spent any time on the daughters, so don't have much info.

Since we're on the subject of this family, I know a little about some of their children:

1. Ann bp 31 Oct 1824 Braddan. She might be the 15y/o F.S. at Gorrey home in Begoade Onchan in 1841 (ages 15-19 reduce to 15).
2. John bp 18 Dec 1825 Braddan. Married Ann Kennaugh 8 Oct 1859 Patrick - 4 children. Lead Ore Miner. Buried 17 Mar 1873 Patrick (Will).
3. Thomas bp 8 Jul 1827 Braddan. Married Mary Jane Bawden 30 May 1861 Patrick - 9 children. Lead Ore Miner. Lost him after 1871 though wife and family are at Onchan in 1881 and she died 1885.
4. Elizabeth bp 29 Mar 1829 Braddan. She's age 30 with parents at Quarterland Patrick in 1861.
5. Isabella bp 11 Sep 1831 Braddan. In 1851 she may be the one age 19 House Servant in Lherby-dhoo German with Boyde family. Perhaps the one buried 7 Mar 1854 Braddan age 22.
6. Sarah bp 6 Jan 1833 Braddan. Married John Cowle 17 Oct 1857 Patrick and may be the Sarah Cowle buried 2 Aug 1859 German age 26.
7. Margaret bp 6 Jul 1834 Patrick. Married Isaac Corkish 30 Apr 1859 Patrick. Issue. Margaret Corkish bd 5 Jan 1902 at Foxdale age 67.
8. William bp 18 Dec 1836 Patrick. In 1871 he is age 34 Farmer of 10 acres living with his widowed mother at Old Road Patrick. I haven't looked for him beyond that yet.