Here's a possible match for the marriage of Bernard and Kathleen from the BMD Index :
Name: Bernard Banks
Registration district: Dublin North
Event type: Marriage
Quarter and year: Oct - Dec 1948
Volume : 2 / Page : 421
There's two separate cross-matches to Kathleen (same year/qtr, reg. district, volume & page), one under her married name (Byrne) and another under her birth name (O'Reilly)
The earlier marriage is proving difficult to locate due to the common names and not knowing an approximate date. Do you know where Ellen fit in the timeline (i.e. eldest, middle, youngest etc) of Kathleen and Joseph's children, or approx.dates for any of the other children ?
Shane