Hi SilkenTom,
Cheers for this but things have moved on since I posted this...
I ended up writing to the secretary at the Church of the Assumption in Ahiohill which is where Roche was PP and is buried. My reason was that whilst there were online baptismal records, many of which were officiated by Roche, there were no marriage records at all. Anyhow she supplied me with the marriage details - 10th June 1834 which was almost a year before the birth of their first child Mary 23rd May 1835. She also said that she would speak to the PP as the company that did the digitising of the archives should have done the marriage records too. I'm not sure if this has been resolved yet.
So I have my Walsh/Ahiohill connection and later documents for Catherine O'Neil (Walsh) give her father's details at Ahiohill (Patrick) and indeed the Tithe Applotment books confirm that in Ahiohill there are only 5 families - 2 Walsh (one being Patrick and possibly a brother) and a Rev. Maurice Roche. Seems pretty conclusive?
As for emigration, James (the father) went first in September 1850, followed a year later by 2 daughters and then followed again a year later in 1852 by the remaining family - all to NYC. Michael was born in December 1850 in Fourcuil - James had left his pregnant wife and 8 children at his sister and brother-in-law's property - Catherine Neill m. John Kingston. The property today belongs to an adopted relative of a descendant of Denis Neill (see below).
I too have tried to use the sponsors' details on the various baptismal records to try and ascertain possible family members as well as the locations. I am reasonably confident that for James, I have identified 2 sisters (Catherine m. Kingston and Elizabeth m. Donovan) a brother Denis (who I already knew about) and I'm almost certain about the Felix. I have other possibilities from the sponsors' details for the children of Kingston and Donovan but I can't be sure with these for now. Locations - Cashelisky, Reenroe, Fourcuil and Drimoleague do almost all border each other including what you noted, so it is highly likely that the various Neills are related but untangling the Gordian Knot is another question. I've tried to do this with a chap called Mark Grace who has done more work on this but so far it's work in progress. He's done far more work on the overall ancestral roots for the various Neills in the area than I have - I've chipped away purely at my lineage.
Finally we have James' father as Patrick born about 1760 Drimoleague - that's it and this is not confirmed - it's merely oral family info. Something I fear may be beyond confirming now?
Many thanks - Michael.