This sounds as if it should be your couple but there are a few discrepancies such as their ages and places of birth but it seems unlikely that another couple with the same names would marry at that time. These 2 married at St Saviour's parish church on 1st July 1891
Frederick Thomason, aged 24, bachelor, occupation Private 1st S L I, living in St Helier, born in Towcester, Northampton. Father Frederick Thomason - Brick Layer
Jeanne Ollivier, aged 25, spinster, no occupation, living in St Saviour, born Lanloup, Cote d'Armor. Father Pierre Ollivier - Farmer.
The witnesses were Albert Huges and Annie Ollivier