Patrice,
Methodism took a lot longer to become established as a separate denomination in Ireland than was the case in England. In Ireland there was considerable resistance to separating from the Church of Ireland. It was 1816 before Methodists could conduct their own baptisms. However because of continuing loyalty and other factors, many Methodists continued to use the Church of Ireland for sacraments for many years after this date and it was 1871 before all Methodists routinely performed their own baptisms.
For marriages, the earliest ceremonies conducted by a Methodist Minister that I am aware of in Ireland, date from 1835 (Belfast Donegall Square). However in the mid 1800s there were only a few Methodist Ministers (Methodism relied heavily on lay preachers). So the shortage of Ministers contributed to the continuing practice of marrying in the Church of Ireland.
So to summarise, you are unlikely to find any Methodist baptisms much before 1830. Few marriages before the 1840s and only a few for many years after that. If there are no Methodist records in the location you are interested in, I would search the Church of Ireland instead, as that’s the most likely place to find the relevant event.
Looking for Methodist meeting houses in Drumkeeran I see one in Pettigo (Wesleyan Methodists). They have baptisms from 1835 and marriages from 1872. Also in the area is a Meeting House at Terwinney with baptisms from 1829 and marriages from 1878. Copies of both sets of records in PRONI in Belfast.
So, given that your two ancestors were presumably born before 1829/1835, you should search Drumkeeran Church of Ireland instead.
If looking for graves, likewise try Church of Ireland graveyards. Most Methodist Meeting Houses have no graveyard and use the Church of Ireland (which is open to all denominations) instead.