Ballykelly is in the RC parish of Seapatrick. Their parish records start in 1843 (baptisms) marriages (1850) and burials 1833- 1880. Few RC parishes have burial records so you are lucky there. The RC parish records are on-line free on the National Library site:
http://registers.nli.ie/parishes
There appear to be 3 chapels in the parish.
You could contact the local parish priest for advice on likely graveyards. People aren’t always buried where you might expect them to be. Also bear in mind that the majority of the population couldn’t afford a gravestone.
http://www.parishseapatrick.co.uk