The originals of Irish BDM certs are not viewable on line. There are some pay to view sites where you get transcripts but they don’t all have all the details eg addresses and witnesses, so if you want to see the full details on the certificate you have to order a copy. I use GRO Roscommon because they offer a photocopy option, which is cheaper than a full formal certificate, and it eliminates the possibility of transcription errors. Provided you give them accurate information, and they don’t have to do any searching, a photocopy only costs €4.
Go to the GRO Roscommon website: www.groireland.ie/Download the application form you need, and complete with the information you have, including the location, year, quarter (if there is one shown), Volume & page number. Put that information on the lines for date and place of the event etc. Don’t worry if you have to leave some boxes blank, eg PPS number. Be sure to tick the box marked photocopy. You then either fax or post the form off (there is no e-mail option for photocopies, or for any certs pre 1.1.1922). Their turnaround time is 7 to 10 days plus however long the post takes.
GRONI would also have these certs but they are £14 each from them. PRONI would not have the births. It might have baptisms and the marriage (if you know the churches they attended, and the relevant records have been copied).