Surnamedb.com has Gregg as originating in Scotland and Hadley in England. Do you have any early Gregg or Hadley first names in your family? You may want to go to familysearch.org and enter each of the two surnames and enter Ireland as well. There are lots of results in different parts of Ireland for both.
Greggs have lived in Ballymena, Killala, Stranorlar, Sligo, Antrim, Magherafelt, and Larne.
A number of Hadleys lived in Belfast, other locations include Dublin, Waterford, Clonygowand of Kings, Enniskillen, and several in Sligo.