Which member of the family are you researching?
You are using Clarendon Street as the marker but there are several years between the records where you have it.
There are Byrne families in 1901 and 1911 censuses in Clarendon Street and as you say it is a common name.
Which records do you have where Margaret is described as ‘dull-witted’ and ‘mentally deficient’. The censuses don’t record anything like that for her.
Sorry, this is all questions - you also mention Military Archive records - who is that for?