my mothers family is from dublin, and unusually in that they have a documented history (a 3 volume set) of the family in the city of dublin for 500 years

That is unusual indeed: in this country living memory is the limit of most people's knowledge of their ancestry. And in another way - very few people's ancestors lived in Dublin. This country having been overwhelmingly rural until recently, most Dubliners are second- or at most third-generation blow-ins.

Errigal Road in Drimnagh, eh? And grandad was in the IRA? Or more likely the Free State Army.