Ed,
You mention that Deborah Harland was descended from Ezekiel born in 1679 in the parish of “Donnahong”. There isn’t a parish of that name in Co. Down. There are 3 that start with “Don”. Donaghadee, Donaghcloney & Donaghmore. So those might be his likely place of origin. Having said that, his family probably isn’t of Irish origin anyway. MacLysaght’s “The Surnames of Ireland” states that Harland “appears in the 1664 hearth money records of Co. Armagh and has since been continuously in that county and adjacent areas. It is an English toponymic (Yorkshire & Devon).” MacLysaght thinks that the Harlands came from Yorkshire or Devon, some time in the 1600s. The Harland family had therefore probably only been in Ireland for a short period before departing onwards for the US. (That wasn't uncommon for incomers from England, Scotland & Wales).
I can’t find any authoritative source on the Allender name (though I sense it may be Scottish). It is not a native Irish name. MacLysaght doesn't list it However the vast majority of migrants from Ireland to north America in the 1700s were descendants of Scots, English and Welsh settlers to Ireland who arrived there in the 1600s, decided it didn't suit them for a variety of economic and political reasons and so moved on again. In contrast, native Irish (if that’s the correct term) didn’t start leaving in significant numbers till the 1800s. So Allenders leaving in the 1700s fits with that background.
Kirkwood is also a very Scottish name. So that, and the timeline, makes me think the Allenders were a Presbyterian family originally from Scotland.
The majority of emigrants from Ireland to North America in the 1700s were Presbyterians (of Scottish origins). Migration started in earnest in 1718. Background here: https://www.ancestryireland.com/wp-content/uploads/2017/08/The_1718_Migration.pdf
There are almost no records in Ireland of folk from the 1600s or 1700s and the chances of finding any of your families are not high. (None of the parishes in Down that the Harlands may have lived in have any records for that period).
Going backwords, most Irish research comes to a stop around 1800 and if your ancestors left before that, it is very difficult indeed, unless they were very wealthy or notorious. Few records exist.
