Hmmm.
Took a while but I finally found an authoritative statement of the forbidden degrees of marriage (of all places, on the web site of His Majesty's Revenue and Customs! -
https://www.gov.uk/hmrc-internal-manuals/tax-credits-technical-manual/tctm09380 )
List of prohibited relationships for marriage and civil partnerships
Throughout the United Kingdom (UK), Guernsey, Jersey and the Isle of Man, the law prohibits certain blood relatives, step relatives and relatives-in-law from getting married or registering as civil partners. Unless they fall within the exception below a person cannot marry or become civil partners with their:
child
adoptive or former adoptive child
child of former spouse or civil partner
parent
adoptive or former adoptive parent
former spouse or civil partner of parent
parent’s sibling
sibling or sibling’s child
grandparent
former spouse or civil partner of grandparent
grandchild
grandchild of former spouse or civil partner
In the above list “sibling” means a brother, sister, half-brother or half-sister.Under these rules, John James and Jamsie would clearly not be allowed to marry (assuming that Agnes Dunlop really is a red herring of course).
What isn't absolutely clear (to me, at least) is whether this identical list of prohibitions applied in the 1890s.
