It's lovely that you are helping your wife find out more about her Igoe ancestors! During Griffith's Valuation (1847-1864) there were 44 households
by that name, so it's not a very common name.
Before 1864 records were kept in the form of church and parish records; while some of these have regrettably been lost over the years, all the surviving records have been sorted into county-based genealogical centres
. This means it is important to know where the ancestors you're looking for were from because that way you can get in touch with the right centre. Do you happen to know where on the island they emigrated from? This might lead to a clue to where they were from.
You can also browse through the church records
to see if there are any relatives or clues. Do you happen to have any names of relatives of John, Bartholomew or Bridget?
I hope this was helpful, and that some of the experts here can provide you with more resources. :)