re: John Belshaw and Fanny McRoberts married about 1832
Compulsory civil registration of non-Roman Catholic marriages began on April 1st, 1845. The registration of births, deaths and all marriages commenced on January 1st, 1864.
Your only chance of finding their parents, would be to contact the local Church for a copy of the marriage cert.
If they have a record, that would probably show the names of the Fathers of the couple.