Hi Bernard,
I will see can I help you any further. I looked at Robert's marriage in 1892 and he states his age was 37 which fits with the date of birth that Patricia has included above. On this marriage cert it states that Charles is dead and that he was a shoemaker, this is from the civil records on https://civilrecords.irishgenealogy.ie
I was unable to find Charles death that I could identify because I am unsure as to where he may have been living, nor could I find a marriage for him to Ellen Kelly, but that may just because the records are not transcribed or missing. Do you think that Robert was the only child to Charles and Elizabeth? I did find a Mary Sheridan born to a Charles & Mary in 1865 & John in 1869, but in these record he is listed as a blacksmith, the names are common, so unless you have further information it is difficult to be sure this is the same family. Do use the records available on https://civilrecords.irishgenealogy.ie and on https://genealogy.nationalarchives.ie, you may be able to widen out the family tree which would take you back further. It might be worth taking out a subscription for even a short term on https://www.irishnewsarchive.com and look up the Anglo Celt, sometimes you will find court cases, sales, funerals etc that may give you a little more about the family, particularly if they belonged to societies.
You could also contact Cavan Genealogy as follows, they will do research for a fee.
Cavan Genealogy
1st Floor, Johnston Central Library, Farnham St., Cavan
Tel: +353 (0) 49 4361094
Email: cavangenealogy@eircom.net
Best of luck with your research and if you wish to check anything with me please do.
Regards Carmel O'Callaghan