Your Irish info was sketchy indeed. This caused me to work hard.
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.
Note 1 - Without a KNOWN county, the chance of an ancestor's rcds NOT being in this database is AT LEAST 35%.
Note 2 - Only 1/2 of Co. Cork's rcds are in this database.
Note 3 - The RC church kept control over most parish rcds from Tipperary (north). These are ONLY available thru the Tipperary Family History Research center at a substantial fee (regardless of outcome).
For John Slattery M 1853 +/- 4 yrs somewhere in Ireland, I found 32 rcds.
For Marg(aret) Gorman M ditto, I found 26 rcds.
By comparing the yr/cnty lists, I found there were potential matches in 1851 LIM, 1852 LIM, 1854 LIM, 1855 TIP, AND 1855 GAL.
Comparing the parish M rcds from each of the above counties, I found matching M rcds in 1854 LIMerick in the parish of Caherconlish. These are LIKELY for your ancestors - no guarantee. A view of the detailed rcds SHOULD show the marriage was to each other. If so, this will validate the rcds. The view should also show their parents' names and other info.
Potential siblings born in Caherconlish, Co. Limerick are: Ellen 1854, and Elizabeth 1857.
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.