Hi Pat,
my only suggestion to you is re the Griffiths Valuation.
Please bear in mind that the Griffiths is a list of the people that were responsible for paying the rents on certain plots of land. That doesn't mean that the person actually lived on that piece of land but may just have farmed it.
For example you may see 3 Thomas Harron's in close proximity in your search area in Donegal and at first glance you may think there were 3 (and yes this may be the case) BUT there may have been just one Thomas who was leasing 3 different plots of land.
Also, never trust 100% what is written on certs. When you are going back that far and dealing with a lot of illiteracy, it can sometimes be 'pot luck' as to what was filled in. People sometimes guessed the age of the person that they were registering a death for. They could also make the mistake of giving their own address as opposed to the person's address.
Maybe, if you retrace your steps with just one branch of your family (it can be all to easy to do too many branches at one time and get confused).
Maybe if you restart with your grandmother who states that she was from Ballynakillew. If you wish to post what details you have for her and then we can help you work backwards.
Hope this is of some use !
Tara