I believe Johanna, Terence, Mary Ann and Ursula arrived in NY on July 10, 1850 from Limerick on the "Barco" under the name of O'Conner. The ages for the most part match the 1860 census. David was not among them which probably means he came over earlier.
It's possible, but by no means certain, David and Johanna are buried in the same cemetery as Ursula. I believe there is an archives for the Pittsburgh Archdiocese. They may be able to help you find something on them.