Hiya Matty,
I regret I am unable to check the 1901 census at this moment.
I have an 1852 Directory of Belfast and the Province of Ulster. It lists six Gelstons in Belfast.
They are -
Hugh Gelston, wholesale wine and spirit store, 35, Ann Street and Upper Church Lane
James Gelston, medical practitioner, Keenan's Place, Ballymacarrett
Miss Gelston, dressmaker, 11, Queen Street
Samuel Gelston, 11, Queen Street
Samuel Gelston, wine and spirit merchant, 17, North Street (Res. Rosstulla, Whiteabbey
William Gelston, merchant and tobacconist, 40, Tomb Street - 8, Great Georges Street
The online Directory of Belfast and the Province of Ulster 1880 shows nine Gelstons
Hugh Gelston, grocer, spirit & provision dealer, Strandtown
J. Gelston, 15, Cliftonville
John Gelston, Knock
Joseph Gelston, 102, Durham Street
Mary Gelston, 20, Landscape Terrace
Samuel Gelston, Knock
Gelston & Co., salt refiners, coffee roasters, tobacco and snuff manufacturers, 62 Great Patrick Street
S. Gelston (Gelston & Co.), 6 Clifton Terrace, Duncairn Street
http://www.lennonwylie.co.uk/alphanames1880gh.htmThree Gelstons signed the Ulster Covenant in 1912
Mary, 26, Stranmillis Road
Georgina and Jane, Ballyhanwood, Knock
http://www.proni.gov.uk/ulstercovenantsearchThere is also an area in the Strandtown district of Belfast called Gelston's Corner.
I know this area well as I lived a couple of miles away for many years.
http://gelston.org/art990317.html All the Best, Chris