hampan,
Researching in Ireland in the 1700s is very hard going due to the general lack of records. If you don’t know where they lived it’s a needle in a haystack. Ideally you need to know the person’s exact denomination and the townland or parish they lived in to have any chance of finding them, and even then there may not be any records for that location.
You do at least know your ancestors were Presbyterian. The majority of migrants from Ireland in the 1700s were Presbyterian, and were in the main descended from Scots who had settled in Ireland in the 1600s. There were probably about 200 Presbyterian churches in Co. Antrim in the 1700s but sadly only 6 of them have any records for that period. The rest either didn’t keep any or they have been lost over the years from fire, damp, carelessness and other hazards. (The Presbyterian records that do survive for the 1700s are copied and held in PRONI, the public record office, in Belfast. Personal visit required to view them).
Possibly DNA testing may be a way of matching with others who have additional information about where the family originate. Family Tree DNA reportedly has more people with Ulster roots than any other company. That obviously increases the chances of finding a match. You might want to try them or, if you have already tested, you can transfer your results to them for no fee.
The North of Ireland Family History Society is running an Ulster DNA project in conjunction with FTDNA and can offer testing kits at a reduced price. http://www.nifhs.org (Go to DNA project on the website).