You already have:

(1871) Carmodyl Moar (Mona House), Ballaugh RG10/5772 f.92 p.11 sch. 58
Augusta M.C. Cavendish governess un 20 Governess in Advocate’s family England near London

Augusta Adeline Mary Cavendish married Francis Edwd Harrison 28 Oct 1872 Ballaugh

The 1871 census has Francis Harrison also in Ballaugh with a birthplace and date of Southport c. 1841:

(1871) Ballaterson Moar, Ballaugh, IOM RG10/5772 f.110 p.9 sch.43
Frances E Harrison h unm 30 farmer of 65 acres emp. 2~~ Southport, England
[sch.42: Dollagh Beg – John Corlett; sch.44: Ballaterson Moar – Daniel Corlett]

Which points to him in 1861 with his sister in Yorkshire, presumably learning the trade:

(1861) Reedness Hill, Reedness, Yorkshire RG9/3527 f.46 p.21 sch.123
John Egremont h m 36 Landed Proprietor & Magistrate Yorks, Warmsely
Francis Maria w m 34 Cheshire, Cheadle
3 sons
Francis E Harrison Brother-in-Law u 21 Agricultural pupil Lancs Southport
6 house servants

John Egremont mar. Francis Maria Harrison 1st qtr 1846 Ormskirk, Lancashire vol.21 p.431 Freebmd

Francis Edward is with his parents in 1851:

(1851) Summer Hill House, Conchan, IOMHO 107/2525 f.54 p.58/9 sch.187
Henry Harrison h m 68 JP of Lancashire & Cheshire b. England
Elizabeth w m 48 “
Charles ?F s u 27 “
Clara Jane d u 19 “
Robert E s u 17 “
Henry John s 12 “
Francis E s 11 “
3 servants

Could this be the right marriage for his parents? -
Henry Harrison mar. Eliza Mann 24 Dec 1820 St Peter Leeds, Yorkshire

Brian Lawson has a burial that looks like Augusta's husband in 1880, and a will for him that might be interesting:

Burial: HARRISON, Francis Edward Stant 40, Ger, 4 Oct 1880
Will: HARRISON, Francis Edward, 1880, Bra, E 148 0106491

You presumably have Augusta, widow, in German in 1881.

She is at the old Harrison home at Summerhill in 1891. I haven't checked to see who was there between 1851 and 1891:

(1891) Summerhill, Douglas RG12/4689 f.133 p.26
Augusta Harrison h w 40 living on own means England
Francis H. “ s s 17 engineer - fitter Ballaugh
Elisabeth H. “ d s 16 Lezayre
Augusta A. “ d 14 Lezayre
Jane E. Craine visitor s 35 Ballaugh
Mary Harrier “ 8 England
(Servant)

There is a burial and will for Augusta in 1892:

Burial: HARRISON, Augusta Adeline Mary 43 Ger 7 Jul 1892
Will: HARRISON, Augusta A M 1892 Dgs 184 0106515

Her son married in 1897:

Francis Henry Harrison mar. Annie Frost in Salford 2nd qtr 1897 vol.8d p.74 freebmd

and had their first child in 1898:

HARRISON, Francis Cave. 6 May 1898 Bal s/o HARRISON, Francis Henry & FROST, Annie [Lawson index]

(1901) Ballaquinney beg Farm House, Marown RG13/5308 f.5 p.1
Francis H Harrison h m 27 farmer Ballaugh
Annie “ w m 24 England
Francis C. “ s 2 Isle of Man n.k.
(servants)

(1901) 137 Cecil St, Moss Side, Lancs RG13/3711 f.136 p.15 sch.91
Mary L. Kibble h wid 63 Living on own means Lancs Manchester
Archibald A.N. grandson 7 “
Elizabeth H. Harrison cousin s 25 Isle of Man
Augusta A “ “ s 23 “
(servant)