Sancti, as you can see from the address, this is one of the John's you mentioned from the VRs. The 1915 VR is his last as I couldn't see him after (as we now know, he died the following year).
Diana, I think everything is covered on this cert:
His two marriages to Mary Ann Black and Charlotte Campbell
The issue of his parent/s. Although married twice and giving the same info re his parents, John is fact was the illigitimate child of Bridget Thomson. If anything, his reputed father likely a Kennedy (given John's given surname on his 1871 census entry with his mother, half sister Susan and his mother's family).
The birth you have in 1868 with mother showing as Bridget Thomson is correct. Birth registrations always give the mother's maiden name.
So, apart from censuses for him for 1891-1911, you now have all the other key details I think.
Monica