Are you sure that you have the right 1851 census?
1851 Queen Street, Campbeltown, Cantyre, Argyllshire,
Hugh McLachlin Head Male 32 1819 Fisher Edinburgh, Midlothian, Scotland
Cathrine McLachlin Wife Female 27 1824 - Argyllshire, Scotland
Flora McLachlin Daughter Female 4 1847 - Tobermory, Argyllshire, Scotland
Agness McLachlin Daughter Female 2 1849 - Tobermory, Argyllshire, Scotland
Niel McLachlin Son Male 0 1851 - Tobermory, Argyllshire, Scotland
1861 Beith's Land, Queen Street, Campbeltown, Argyllshire
Cathrine McLachlin Head Widow Female 36 1825 Laundress Saddell, Argyllshire, Scotland
Flora McLachlin Daughter Unmarried Female 14 1847 Scholar Tobermory, Argyllshire, Scotland
Annie McLachlin Daughter Unmarried Female 12 1849 Scholar Tobermory, Argyllshire, Scotland
Neil McLachlin Son - Male 10 1851 Scholar Tobermory, Argyllshire, Scotland
James McLachlin Son - Male 8 1853 Scholar Tobermory, Argyllshire, Scotland
Colin