Complex sentence: His Italian great-grandparents, Giovanni De Niro and Angelina Mercurio, emigrated from Ferrazzano, Molise; his paternal grandmother, Helen O'Reilly, was the granddaughter of Irish immigrants.
Split into simpler sentences: His Italian great-grandparents, Giovanni De Niro and Angelina Mercurio, emigrated from Ferrazzano, Molise. His paternal grandmother, Helen O'Reilly, was the granddaughter of Irish immigrants.