1. Re John Cash senior.
Where did you obtain the information about death of John Cash in 1870? I looked on Irish civil records site for his death registration and couldn't find it. I searched death registrations for all of Ireland.
Irish Genealogy.ie
https://civilrecords.irishgenealogy.ieOr was it Elizabeth Cash who died in 1870? Re-reading that paragraph in your opening post, the death information could relate to either John or Elizabeth.
Did whoever it was die in Wexford Town/Wexford Registration district ? Where and when did the other spouse die? Who was informant of each death?
When and where did John and Elizabeth marry? Where did you find the information about their marriage? What religious denomination were they? Who were witnesses?
You say John Cash was born "about 1791". Where does this information come from? Have you looked for his baptism? Civil registration of births, marriages and deaths began in Ireland in 1864. Before then you need to search church registers. Many Irish churches don't have registers dating back pre 1800. Some don't start until mid 19th century. Catholic registers are free to view on National Library of Ireland site. If he was Catholic, who were baptism sponsors (godparents)?
I assume that John Cash born approximately 1791 in Wexford was John Cash senior, father to the John Cash whom you say was a famous piper.
What was occupation of John Cash senior? Have you looked for him on Griffiths' Valuation and on Tithe Aplottments?
Re. John Cash junior, aka John Cash, the piper.
You say that he had 2 wives. Are you sure it was the same man? Where and when did he marry each wife? Polly might have been short for another name. Have you found a death registration for either wife? Who were their children? Years and places of births? Religion?
Where and when was John Cash junior born? Have you found a baptism for him? If it was a Catholic baptism, who were sponsors (godparents) ? Did he have any brothers and sisters?
Where and when did John Cash junior die?
Elizabeth Ryan. What is your source for her birth information and for her parents' names?
2. Re John Doran (the one born c.1823)
What is your source for his birth and his marriage?
When and where was the marriage? Have you searched for a church record of the marriage ?
Who were their children? Names, places and approximate years of birth?
Have you searched Griffiths' Valuation?
When & where did John Doran and his wife, Jean die?
What religion were they?
Can you give us dates and places for John Doran, the piper?
Have you done any Irish family history research before?
Answering these questions will save us time in the long -run and may give you ideas for other resources you can try for yourself. Irish civil registration website, many Irish Catholic parish registers, Griffiths' Valuation and Tithe Aplottment Books are all free online.
Finding information about people born in Ireland before 1800 isn't easy and is impossible in some cases. Going back a further generation will be harder still. What I said on another of your threads about problems of pre-1700 English research applies to Ireland pre-1800.