Ok, so I've got my notes sorted now. My great-grandfather Christopher McNickle was one of many children of Samuel McNickle and Matilda Dick, in Elagh. Their family began very soon after your ancestors were born to Samuel McNickle and Jane Sayers, also in Elagh.
When my Samuel McNickle married Matilda Dick he was described as a widower! So I am wondering was the same Samuel married to both woman - did Jane die young and he remarried Matilda? Do u have a date of death for Jane? BUT there is a spanner in the works for my theory - Samuel's father was a Robert McNickle, also from Elagh and your Samuel was from Creggan, Co Armagh. I find it a very strong coincidnece that there were 2 Samuel McNickle's in the small townland of Elagh, and even moreso that one was a "blow-in" from Co Armagh. Pls let me know your thoughts so that I can put my theory to bed.