I need to clarify a few items. Was Margaret Ann Tasney your great-great grandmother? Is John Tansey the name of your great-great-great grandfather and when was he born approximately?
The surname McCool is not a Galway surname and is more likely found in Co. Donegal or Northern Ireland counties. I think your great-great-great grandfather left Galway and met Catherine McCool. Possibly they met in the Isle of Man. Have you checked the 1901 census in England?
The Glenamaddy RC church records start in 1838 and when I searched the subscription site Roots Ireland, I did not find a John Tansey record but there were John Tansey records in nearby parishes.
Let me know.