Griffin relatives

Hugh Griffin and Margaret O'Connor were married and had 3 sons, all of whom came to America and settled in Washington, DC.  I have looked at Griffiths Valuation and have found  Hugh Griffin, John Griffin, Martin Griffin, Mathias Griffin  and a Mary Griffin in Newtown, Moycullen.  How do I know if this is the same Griffin family?  Looking for a marriage certificate for Hugh and Margaret or a baptismal record that may show Hugh's parents.  Hugh born c. 1799 d.  He died in 1869 in Washington DC. His tombstone reads that he was a native of Galway, Ireland and died at age 74.  His son, Martin 1832-1909  was born in Moycullen and came over first in about 1852-1854.  Hugh, Margaret and sons Thomas and William came together about 1854.  In Washington DC, Thomas married Mary Mulkerins of Moycullen as stated in his obituary.  Would there be any church records that still exist?  I was told that the Griffins left no relatives in Ireland.