« Reply #21 on: Wednesday 28 November 18 00:37 GMT (UK) »
What connection, if any, is there between Elizabeth Campbell or Robb and Margaret Campbell?
I think I can answer that one 
Margaret Campbell died in 1864 - her death was registered by Alexander Robb (son of George Robb and Elizabeth Campbell), and he is noted as Margaret Campbell's grand nephew, so Margaret Campbell was Elizabeth Campbell's aunt.
Margaret's parents are noted as James Campbell, quarrier, and Janet Campbell (ms Cullen). There is a suitable baptism of a Margaret Campbell to a James Campbell in Aberdour on 28 Oct 1779. There is also a baptism for an Alexander Campbell to James Campbell and Janet Cullen on 18 Oct 1772, which matches the age of Elizabeth's father, Alexander.
On Elizabeth Campbell's death registration, her parents are noted as Alexander Campbell, farmer and Janet Gordon, domestic servant, so I think it's quite likely that Alexander didn't marry Elizabeth's mother.
Ruth
I agree with that line of deduction, and I had previously come to the same conclusions. A further bit of deduction/guesswork led me to believe that the two witnesses to Margaret's 1779 baptism (John & George Campbell) could well have been James' brothers - all three were quarriers. This ties in with another Margaret Campbell who was baptised 18 Dec 1778 in Aberdour, daughter of George Campbell & Agnes Bruce - witnesses James Bruce and James Campbell. The two Margaret Campbells would then have been cousins.
One piece of information that I had NOT found was Alexander's baptism in 1772 - I can't see it on ScotlandsPeople, where did you get the (valuable) information?
ABERDEENSHIRE: Simpson, Robb, Kelman, Gatt, Will, Ling, Henderson, Campbell, Stewart, Gordon
DUNBARTONSHIRE: Smith, Russell, Donald, Meiklem
GLASGOW: Guthrie
RENFREWSHIRE: Gilmour, Pollok, Urie
IRELAND: McIlhenny, McIlhaney
LANCASHIRE: Swainson, Baines
YORKSHIRE: Littlewood, Bastow/Barstow/Bairstow, Nussey, Haley, Wilkinson
WILTSHIRE: Marsh, Golding/Goulding/Golden/Goulden
DEVON: Perry, Hurford
BERKSHIRE: Chandler, Langley, Surman
AUSTRALIA: Poole, Surman, Miatke, Baum
GERMANY: Miatke, Baum