www.irishgenealogy.ie has Dublin city church records. I did a quick look and saw the baptismal records for all four children of Farrell and Susan. Also, saw the marriage record for Bernard Kavanagh ( not Gaffney) and Anne in 1857. All records in St. Catherine's parish.
There are also Dublin city directories online. Here is an 1850 directory. I did not see Farrell or Joseph listed but maybe they are on another directory.