...point me in the right direction with William Patrick Flood born 1926 Dublin North. He left Dublin at the age of 17 moved to Nottinghamshire married Margaret Greenberry in 1947 had four children then moved to Australia.
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What certs do you have on William ?
his marriage cert should show his father's name & occupation, which is one of the clues you need to identify the correct family, you can can use this to confirm a match to his birth cert which would show both parent's names and William's place of birth. Once you have these details you can start searching the BMD Index for possible birth matches for siblings, and order the certs to see if they match the clues, i.e. parents and possibly address, and therefore be siblings for William.
Births after about 1927 on the online BMD Index include mother's maiden surname, which would help narrow down the search if William had younger siblings. Searching for the marriage for the parents can help with the timeline.
These are the Index references for the marriage in Newark district (Lincolnshire / Nottinghamshire) you mentioned in case you need to order a cert :
Marriages Quarter/Year: Dec / 1947
Bride & Groom : Margaret J. Greenberry & William P Flood
Registration District: Newark
Volume : 3c / Page: 679
Shane