I searched the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds are increasingly sparse B4 1840, rare B4 1800. Unless you KNOW the county of origin, the chance that your ancestors' rcds AREN'T in the database is AT LEAST 35%.
For Joseph Murray B 1879 (exact) in Co. Armagh with a father named John, I found 2 B rcds: one church, the other civil. These may be duplicates.
For James Murray B 1892 +/- 4 yrs ditto, I found ditto. Ditto.
For Joseph Murray M 1902 (exact), I found 3 civil B rcds in Co. Armagh, but none in Cavan.
For Marg(aret) Dinnen M ditto, I found 1 M rcd in Co. Armagh.
For John Murray M 1874 +/- 4 yrs, I found 168 M rcds with 4 in Armagh in 1878.
For Marg(aret) Brankin M ditto, I found 3 M rcds in Armagh in 1878. A view of the M rcds MAY give their ages. It SHOULD show their parents' names. If so, this will take you back another generation.
You can search the database for answers to your questions.
Google the Foundation's name to lead you to this database. Register, opt to be notified as rcds are added and browse. Pls post your search results to my genforum msg.