Welcome to RootsChatWe do need to know which area of Ireland the parents may have originated from.
An old message board post from December 1999 - suggests that the parents John McCusker who married a Bridget McKearney Ireland, approx 1830, moved to Scotland had a son born Thomas McCusker August 1851. Have you searched Scotland census ? What information have you already found ?
http://boards.ancestry.co.uk/surnames.odonnell/394.455.457.495/mb.ashxThis would appear to be the family in 1900 Darlington, Beaver, Pennsylvania. Census would appear to say Thomas immigrated in 1875 and was married in 1879. Under McCuster.
Thomas Mccuster 48 Jane Mccuster 39
John P Mccuster 24 Jennie Mccuster 9
Hugh Mccuster 17 William Mccuster 15
Ennet Mccuster 13 Frank Mccuster 10
Ellen Mccuster 8 Marie E Mccuster 1
https://familysearch.org/ark:/61903/3:1:S3HY-6SM7-GN5?mode=g&i=20&cc=1325221Son John McCuster born 27 October 1884 Sandy Creek, Pennsylvania according to U .S. Social Security Applications and Claims Index.
Have you managed to locate any obituries for Thomas or Jane in the USA which may suggest parents names or where they came from ?
Have you followed there children in the USA ?
Sandra