Alison,
Birth registration only started in Ireland in 1864. Prior to that you need to rely on church baptism records. Not all churches have records pre 1864 and of those that do, not all are on-line, in particular Presbyterian records. The most complete set of records for that area are held in PRONI (the public record office) in Belfast. Personal visit required to access their church records.
The 1869 marriage was in the Register Office. Unfortunately that doesn’t give any clues as to the couples respective churches. However Annie (Nancy) married in Monreagh Presbyterian church on 1st August 1893. That might be the Roulston family church. Their records start in 1845. Copy in PRONI. If you are unable to go yourself, you could employ a researcher. Researchers in the PRONI area: http://sgni.net
A witness to the marriage was Mary Jane Roulston.
I looked for a death for David Roulston but did not see one that is likely to fit. This could be Mary Jane’s death in 1890. If it is, then David was still alive then:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1890/06116/4745947.pdf
Note that this lady died in Haugh. I then found this death in 1892 for a David Roulston. I suspect that might be David junior’s father. Informant was David, son, also of Haugh.
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1892/06046/4722534.pdf
Birth of David Roulston in 1879:
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1879/02896/2061177.pdf
Birth of Mary Jane 1875:
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_retur…
Also spotted this birth in the same area for a Mary to Robert John Roulston & Elizabeth McClintock. Did 2 brothers marry 2 sisters?
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1869/03373/2236601.pdf
Here’s the couple’s marriage. Groom’s father was David, a labourer, so I suspect these are siblings. Elizabeth married in St Johnston Presbyterian so that may be the McClintock family church. Their baptism records start in 1838. (Copy in PRONI).
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1867/11485/8221678.pdf
This might be that family in the 1901 census:
http://www.census.nationalarchives.ie/pages/1901/Donegal/Castleforward/Tullyannon/1190603/
Here’s a birth for Rebecca around the right time which points to the above family being the couple who married in 1867:
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1881/02816/2033350.pdf
