No I haven't ruled out either John Couper as I cannot find Death Certificates for the two John Coupers and the two Robert Coupers.
The Marriage Certificate shows:
John Couper, Master Mariner-Merchant Seaman, Father: Robert Couper; Baker & Grocer. Ellen Humble Father: George Humble, Engineer. Witnesses: John & Jane Waugh. Address; South Shields.
Earlier information from Queensferry, Scotland, 1831, showed Robert as a Labourer, wife Elizabeth Ag/labourer, son Robert; Stone Quarryman and John aged then 15, Labourer. This Robert Couper was deceased in 1853 which is also another reason he's not John's father as that would have been noted on his Marriage Certificate. Which is why I queried this information with the Researcher.
It does seem more reasonable that the John Couper born in South Shields is the father to my great grandfather John Robert Couper. The name Fornear comes from Ellen Humble's mother - Elizabeth Fornear. It is still carried on today in the male line.
The 'James Freeman' (1851-1860) Built: Hartlepool - Owner: Robert Couper (s.o.) South Shields 30th April, 1851.
Samuel Couper and James Errington Ritchie, South Shields, shipowners each acquired 16/64ths.
Masters: 7/5/1851 - John Couper; Alfred Cannute Swinfin Couper 10/5/1852 and Edward Charlton 7/3/1854.
The James Freeman was lost near Lemvig, Denmark, on 21/10/1860 when on passage from Hamburg to Newcastle.
John Couper was also listed as Master of 'Maria' on 25/1/1853.
As I sit here typing out this information I have collected it does seem to me that the Coupers of South Shields are more likely to be my ancestors.
Gumball