What he tells me about Nettie/Kitty is that she is supposed to have had special needs and therefore, probably never married. It seems that any information he has comes from his now long-deceased mother.
Firstly thank you for all your help. I followed your link to the 1911 census but that only brings up Michael, Kate and a daughter Mary. I don't see where you get the list of six.
https://www.census.nationalarchives.ie/pages/1911/Waterford/Kilmeaden/Ballycahane/909544/Interestingly lists 6 children/4 living.We have births of 4 (Mary, Pierce, Johannah, Bridget) and know that Pierce and Johanna[h] were alive in 1911. So, who are the two missing children and which of the 6 children died before 1911?