Hi Janet
There really doesn't seem to be any trace of Robert and Margaret after 1861 does there?!
I cannot see a death for Margaret in Scotland searching for a Margaret M*cG*v*n/Sk* (pretty open on the searches!). I would also have thought that given what Robert did for a living, he would probably have left a will but the only one I could find of interest were these two entries on SP:
1 MacGavin Robert 30/10/1901 Coen River, Colony of Queensland, d. 19/02/1900 at The Bend, Coen River, intestate non-Scottish Court SC70/7/5
2 MacGavin Robert 27/12/1900 Accountant, The Bend, Coen River, Coen, Colony of Queensland Edinburgh Sheriff Court Inventories SC70/1/396
However, given the year, it may be too late for Robert.
Have you managed to find any of their children post 1861 to check on marriage or death certs whether parents were still living?
I can see the two google refs that you mentioned but they are both in the late 1880s and there is no sign of Robert after 1861. Still worthwhile following up though if nothing else to eliminate this Robert McGavin. I found these two refs for Dundee City Archives:
Records retransmitted from the National Archives of Scotland
• Justices of the Peace for the County of the City of Dundee 1894-1975
• Justices of the Peace for the County of Angus 1791-1974Might be worthwhile following up to see what info these registers hold.
There is nothing showing for in the English Censuses 1871/81 that I could see but there is certainly the possibility they may have left Scotland after the 1861 census given the lack of death entries for both Robert and Margaret.
Regards.
Monica

Hi Sherlock: The 1874 death also shows on the Wills section at SP:
McGavin Robert 30/07/1874 Blacksmith in Johnstone Paisley Sheriff Court SC58/42/41