The picture is starting to build up for you Steve.
Now you know your grandaunt Margaret Stafford nee Crowley had at least two daughters: Joan (later Cronin) and Molly (later Whelan).
You know from the 1901 census (online) the approximate dates of birth of your grandfather Thomas and most of his family, who lived in Loughnageer.
You know from the 1911 census (online) that at age 20 Thomas was working on Martin Shannon's farm in loughnageer.
You know from the 1911 census (online) that his parents, in Loughnageer, were married 31 years and had eight children. This number implies a marriage in 1880 but as the first child was born around 1885-1886 I would suggest they were married later than this. The name Peter Crowley is fairly uncommon so you may find this record is his
http://pilot.familysearch.org/recordsearch/start.html#marriagePlaceId=1928899&marriagePlaceLoc1=Wexford%2C%20Ireland&searchType=close&givenName=peter&surname=crowley&p=recordResults as it matches the record for a Johanna Whelan marrying at the same time. In which case if you go to the GRO site you can order the marriage certificate which should tell you the names of their fathers.
If you do that please let us now the names and where they were from. Especially if Catherine's husband turns out to have been from Loughnageer not Ballycullane.
Good Luck,
Eileen
