I can't quite say "yes" yet to the Thomas connection until we can match the following:
Burial for a Thomas Gelling at Braddan 1836 age 36 with an associated episc will.
I have two loose Thomas Gelling baptisms very close to the 25 Jan 1801 to WmG & Margaret Kneen:
11 Aug 1799 to John Gelling & Isabella Cavendish Braddan
27 Jun 1802 to Thomas Gelling & Elizabeth Kelley Braddan.
So we have 3 baptisms and 2 scenarios that likely match to 2 of them.

The burial index provides 2 other Braddan burials for a Thomas Gelling within the time period but no ages. In the Gelling burial check of Braddan I did some years ago, I have them both but I couldn't make out part of what was written:
Thomas Gelling late of the ? bd. Jul 20 1803
Thomas Gelling (Tin?) bd. Oct 25 1810.

There's also a Manx born Thomas Gelling hair dresser (married to Ann Charlton 1823 & then to Margaret Bains 1835) in Liverpool in the 1841 and 1851 census's, who appears to be born about 1802/3.

There's a Thomas Gelling who died in 1835 Marown age 32 (source Marown MIs), who married Margaret Quayle 1832. He could match one of the baptisms.

You are correct about the paper mill owner, widow of Robert Gelling who died 1849. The widow died in late 1881.