Im looking for my MacRaghnaills ancestors from Sligo who were defeated by the O'Rourkes and eventually moved to Wexford

My grandfathers surname was Denis Patrick Grennell, we have traced his family line back as far as to Sligo when the family was named MacRaghnaill. We know the MacRaghnaills were defeated and lost their land to the O'Rourkes but we are not sure what year this happened and are looking for anyone who may have any information or links to our family from this area or Wexford Ireland where they ended up. The first settlers from Wexford Ireland to New Zealand came to Dunedin City where I am currently living. I have only been living here for the past year and have visited local cemeteries and the local history center but only found un-named graves covered over by dirt and grass, I am yet to delve deeper into the historical records of the settlers museum in Dunedin to try to find more information about our first family settlers to this city from Wexford. My mother said my grandfathers line is the only surviving line from the settlers that came to Dunedin from Wexford, all other family died and have no more descendents. My grandfather was born in Wellington, North Island, New Zealand. His mothers name was Maud, his sisters name was Patricia, he had other brothers. My grandfather died recently and has only one surviving sister Patricia otherwise known as aunty Patsy. My grandfather said that when he and his sister Patricia were born they had jet black hair and were told that they had Spanish blood. We would like to trace back to his family in Sligo the Grannells who were defeated by the O'Rourkes and try to find if the rumour is true and who is the Spanish man who married into our Irish family in Sligo?? If anyone can shed some light it would be greatly appreciated!!!!