I have some information that I believe to be about this family. The came to america through New York in 1840. It doesn't indicate that Roberts parents were born in Scotland, although many of our Scots/Irish family lore claim that we came from Scotland. :-)
You can find the family I'm referring to on the 1850 U.S. Census living in Brady Pennsylvania.
Siblings of Robert are James b 1837 who may have returned to Northern Ireland and married Mary Kerrigan in 1857. At any rate, neither he nor Thomas were listed in the household on the 1860 US Census. A sister Sarah, b 1839 in Gortnagrace, baptized Christ Church Urney who married a Smiley after 1850 and before 1860. A sister Margaret born 1841 in PA, and brothers William b 1844 in PA, Andrew, b 1846 in PA, and James, B 1848 in PA. Thomas was no longer in the household in 1860, and there was the addition of a little girl named Matilda, born 1851.