Hi, there are a large number of different McDaid families in Derry (mostly from the Bogside). My branch is from Derry although going back a few generations (my great-great-grandfather) was Arthur McDaid and was one of three brothers- one called Bernard, and one called Patrick. Patrick and all his subsequent family lived and were born in Derrora townland (near Letterkenny). Arthur and Bernard's family were all in Derry although remember Derry was part of Donegal not so long ago! the border only went up in the 20th century.....
Not sure if this is any help Linda