possibly interesting record for you from the 1911 census...
at number 7 Ravensdale Rd, North Dock there is
Charles (age 42) and Sarah Murphy (age 28) - Charles born in Co. Wexford, Sarah in Dublin city
two children listed, Charles (17) and Marie (8 mon)
Charles born in Wexford, Marie born in Dublin City
married just two years, so maybe a 2nd marriage for Charles. They could be connected to Nicholas - same house as Nicholas and Co in 1939, and has Murphy's from Wexford...
census record :
http://www.rootschat.com/links/06oa/Shane