Hi Allstar, the surnames you enquire about are spelt in a number of different ways. Laverty is indeed sometimes Lafferty and while the 'v' is used in most records I can recall that some years ago a cousin of mine obtained a copy of the entry of death and Mary was noted as "Lafferty". In the days when full reading and writing wasn't something you could take for granted it is not surprising to see this. I also note that Flynn/Flinn/Flin are common variations and the name is completely mistranscribed in the 1881 census as something completely different.
I am pleased to note that GG Grandfather Robert Flynn's occupation was given as embankment labourer. Presumably this means he must have been employed on some sort of canal project near Wigtown?