I've just determined that the first child of John Gelling & Isabella Cavendish (md 18 Nov 1788 Braddan), who is the Mary Cavendish born prior to the marriage, is the Mary Gelling that married Charles Lawson 11 Apr 1807 Ballaugh.

They had a single child Mary bapt 26 Apr 1808 Ballaugh. Mary married Thomas Cottier 22 Jun 1833 Braddan. This couple had 2 children in IOM (Catherine Lawson 1834 & Mary Ann 1836), then went to New York where 2 more were born named Martha Matilda Cottier 1839 and Thomas Lawson Cottier 1841. Soon after the 1841 census they must have come back because husband Thomas is buried in 1843 at Ballaugh. Mary Cottier als Lawson appear in the 1851-1871 census's and it looks like she's buried 1877 at Braddan. Youngest son Thomas Lawson Cottier went to Liverpool, married 3x and died 1903. Martha had an illeg son but remained unmarried and is buried age 42 Braddan in 1881. I can't find the first 2 children, so perhaps they died young in NY?

Here are Charles & Mary Lawson:

1841 census at Mill Easement, Ballaugh HO107/1463/4 3 28 pg 7 (464355)
Charles LAWSON 59 Ag Lab E
Mary LAWSON 53 Y

1851 census at Mill Rent, Ballaugh HO107/2523 383 pg 11 #40
Charles LAWSON, Head Mar 69 Ag Lab & Tailor, b England
Mary LAWSON, Wife Mar 62, b Isle of Man Braddan
Mary COTTIER, Daur Wid 43, b Ballaugh
Martha COTTIER, Grand Daur 11 Scholar, b New York America
Thos COTTIER, Grand Son 9 Scholar, b New York America.

1861 census at Glen, Ballaugh RG9/4411 7 pg 8 #36 (543279)
Charles LAWSON, Head Mar 79 Tailor, b England
Mary LAWSON, Wife Mar 72, b Isle of Man Braddan

Burial: LAWSON, Charles 79 Bal 13 Nov 1861
Burial: LAWSON, Mary 77 Bal 7 Nov 1864
Neither are on Brian's will list.