James Gerrard 1803 - 1863 and Isabella Marshall 1801 - 1872

This is a summary of what (I think) I know about James and Isabella.
James Gerrard was born on 30 June 1803 in the parish of Barry, Angus County, Scotland. He was the son of miller George Gerrard and Jannet Fyffe. James was, as far as I know, the fourth of seven children.

At some point he came south to Newcastle-upon-Tyne, Northumberland, England. I can't find him on the 1841 census in England or Scotland, but in 1845 he was named as the father of Margaret Gerrard on her birth certificate. Margaret's mother was named as Isabella Gerrard formerly Marshall.

By 1851, the family, consisting of James, Isabella, Margaret and Mary Ann and John Stewart were living in Whickham, Co Durham, England. Mary Ann and John are listed as daughter and son of James, but I suspect that they are actually Isabella's children from a previous relationship.

In 1861 the family were back in Newcastle, living in the Elswick area. James and Isabella were enumerated on the census with their daughter Margaret, and a visitor, Mary A Moffatt - I think this is Mary Ann Stewart, now married, visiting her mother.

James died on 18 July 1863 of phthisis (probably tuberculosis). He had worked as a miller all his life and the flour dust may have contributed to his relatively early death.

Isabella was born around 1801, according to the 1871 census in West Silverton, Northumberland. As with James, I haven't yet found her in 1841. In 1871 following James' death she was living with her now-married daughter Margaret and her family. Isabella died on 23 August 1872.

The problem with this story is that there are so many gaps. I can't find a marriage record for James and Isabella, can't find either of them in 1841, can't find an earlier marriage for Isabella, and can't find a birth/baptism record for Isabella Marshall anywhere. And I can't find a place called West Silverton in Northumberland. The whole thing is further complicated by the spelling of the surname - I think it's different on nearly every document I have. So far I've spotted Gerrard, Gerard, Girard, and Jerrard. I've clearly got a lot of work to do here.