Hi again Martin,
The records for the family should exist, they are well beyond the introduction of Civil Registration. However I have been looking and have had little luck so far apart from the fact that James 1903 is on the 1911 census so he hasn't disappeared completely.
Here is one record for you, the marriage of Ellen Connor the sister of Mary Ellen.
This death record for Mary Donnelly, I assume, mother of Mary Ellen seems to indicate another son, James, he was present at her death.
Irish Genealogy added new records yesterday and everybody is on it making it really slow to view records. I'll keep looking for you but I'll leave it at that for now.