Hi Laura. I can understand getting mixed up with all the Johns. I have a lot of data on Gellings and have figured out most of it, so can help you I think.
Stanley Tynwald Gelling lived 1852 to 1928. He was an Iron Miner in Dalton in Furness Lancs in the 1881 census, missing in 1891 and 1901 though his wife Amelia/Emma was in Ballacraine German, then they are at the Schoolhouse in Braddan in 1911 where his son John William was Head Teacher. The UK Incoming Passenger Lists on Ancestry has "Mr. S. Gelling 50 Engine Driver" arriving to London from Sydney Austr on the "Oroya" 9 May 1903.
My notes say he is the great-grandfather through son John, of Rosemary Derbyshire, reference Manx Bulletin Board 11 May 2009. I haven't checked this but I think I recall some discussion about him then. With a middle name like his, he's easy to remember.
His parents were John Gelling (abt 1800-1875), a Miller, & his second wife Alice Collister (abt 1811-1858), md 21 Jun 1847 St Nicholas Liverpool. Alice's father was Silvester Collister, a stone mason.
Grandparents were Robert Gelling (1779-1835) of Ballagrawe Marown and Ann Kelly (1775-1836). They married 3 May 1800 Braddan. 7 children. Ann Kelly's parents were Robert Kelly (ca 1716-1793) of Ballabrew & Elizabeth Lewn (ca 1740-1802), md 1763 Braddan.
Great-grandparents were Robert Gelling (1744-1807) and Jane Kelly (ca 1745-1808) md 22 Sep 1770 Braddan. 9 children, 8 lived. He was a Miller of Ballagrawe Marown. Jane Kelly's parents are not known.
Great-great grandparents are John Gelling (1722-1812) & Catharine Killey (1717/18-1806) of Ballamillaghyn, md 16 Jun 1739 when he was 17 and they had 10 children, 9 lived. They were married over 66 years which is amazing for the time. Robert above was their second son. They have been discussed several times in the past here. The number of descendants is huge. Catharine Killey is the daughter of Philip Killey (ca 1690-1763) & Ann Clucas (d 1755).
3xg: John Gelling (1690-1736/37) & Ann Moore (1695-1748), md 7 Dec 1721 Braddan. Above John was their eldest and only living son. Ann Moore is d/o Thomas Moore & Ann.
4xg: John Gelling (1669/70-1723/33) & Susanna Moore (ca 1660-1731) md abt 1687 when John was 17. Above John was their only living son, but there was an illegitimate son (also named John) by Ann Kneale. b 1705. He was exec of his father's will and had a big family of his own at Ballig, Marown. Susanna Moore is d/o Capt John Moore of Santon.
5xg: William Gelling (ca 1630-1683) & Joney Christian (ca 1630-1688) of Ballamillaghyn. They had 7 daughters followed by a John who died, and finally the above John in 1670.
The history before William is murky but a William Gelling will of 1663 left "his brother's son William Gelling" his quarter interest in Baldell milleat. I suspect his [deceased?] brother's name was John. That's as far as I can go.
I haven't checked Ancestry to look at your tree.
Hope this helps,
Best wishes, Eric.