My great-great-grandmother, Bridget McAndrew, was born in the parish of Killasser in County Mayo, circa 1800. That's several parishes to the southeast of where your McAndrew's lived, so we are probably only very distantly related, but I can give you some info about the McAndrew's which may be of interest.
Before doing that, however, I thought I would share a tip I learned while researching my own family. In the time period where you are searching, the process of re-establishing Catholic churches was still underway, and not all rural parishes had their own church building yet. Where that was the case, people were sometimes baptized or married in a neighboring parish. As Miriam pointed out, the parish records for Ballycastle only go back to 1864, but the next parish to the south, Kilfian, has records going back to 1826, so you might find records for your family there, especially if they lived near the parish border. If you want to check that out, here is a link to the parish records for Kilfian, and you'll see an interactive map there which will let you move to other nearby parishes: https://registers.nli.ie/parishes/0749
On that map, you can also see the parishes of Backs and Attymass to the southeast of Kilfian. That is what one could call the "homeland" of the McAndrew's (my ancestor's parish, Killasser, adjoins Attymass to the southeast). In Irish, the surname McAndrew is Mac Aindriu. The McAndrew surname was adopted by a branch of the Barrett family in Mayo. The Barrett’s were an Anglo-Norman family which became fully Hibernicized. The McAndrew’s became like an Irish sept, having a well-defined territory on the eastern side of Lough Conn (the general area of Backs and Attymass). In the seventeenth century they occupied half a column of the large page index of the Mayo Book of Survey and Distribution (they also appear in it under the synonym FitzAndrew), and all sixteen of the Mac Andrew births registered in 1890 in Ireland were in Mayo. In Griffiths Valuation, there were 232 McAndrew’s listed in all of Ireland, of whom 186 were in County Mayo, and 19 in adjoining parts of County Sligo (which adjoins both Attymass and Killasser).
There were also some McAndrew’s in County Kerry, whose presence is indicated by the place-name Baflymacandrew in the Tralee area. They are believed to have been a branch of the Fitzgerald’s whose descendants later resumed their original patronymic. At one time, MacAindréis, anglicized as MacAndrew, was adopted as a Gaelic patronymic by the Scottish family of Ross, but their descendants generally later resumed the surname Ross,
