Wow! It looks like your grandmother Catherine may be the sister of my grandfather Thomas. Most of the facts match up except for the G grandfather name which was Stephen J. Finn (if you were unable to confirm). If I'm correct on this, your grandmother Catherine married a Forsythe.
If I'm not - here are my Finn facts:
Thomas Finn married Margaret Burke (b around 1850) in Galway. They had 8 children of which I only know of Stephen J (my G Grandfather)(b 1870), Edward, William, Martin and Margaret. They emigrated to the US in 1898-1900. Stephen landed in Boston, then went to Connecticut, then to Elizabeth, NJ where he settled and married Margaret C. Tully.
They had the following children: Thomas (my grandfather, B 1906), John J., Catherine, Margaret (died in infancy), Martin, Stephen and Robert.
Margaret Tully Finn died an early death at the age of 43. Stephen worked at Singer Sewing Maching Co, then the Elizabeth School system, and he also owned a bar! He died in a fire at home in 1945.
Please let me know if this matches up!