i found the 1851 census on freeCEN website
in 1881 janet hunter age 60 and her son alfred hunter age 15 are visiting the married daughter mary ramsay(nee hunter) age 24
middle names(parents george hunter and janet hunter)(from the IGI)
alfred tulloch hunter born 18th oct. 1865 leith
james gale hunter born 19th nov. 1860 edinburgh parish
as Sancti has already noted the next step would be to find george hunter's
death cert.
looking at scotlandspeople website(and given that you have him on the 1891
census) i found -
george hunter death 1891 leith midlothian born c1820
perhaps you can check with your other sources to see if they have that

ev