Geoff,
I am also sceptical of the Grantham marriage. I also don't believe it is right. My family are from Louth which is only 20 miles or so from Swallow. Grantham is too far away.
Perhaps there aren't two wives. On the 1891 census Emma was the wife & in 1901 Jane was the wife. It just so happens that three children appear in 1891.
Born in 1888,1889 & 1890. Then there is a six year gap until 1896 & 1900 ish. My Great Grandmother was the 1896 girl.
I must admit I presumed Emma had died but I may be wrong.
I am revisitng this link after many months of time away from it & for some reason or another I actually have Jane as Jane Stephenson

This may be wrong now I look at it again.
Does this help at all

Thanks
Ian