Possibly death of Thomas Nevin's first wife Winifred, his return to Ireland then remarrying caused the family to fracture so that his children didn't ever hear much about their America relatives.
Problems with finding birth details for the children are registration only started 1864, ages unreliable in later records, baptisms not easily found yet, locations could vary if family moved because of father's occupation.
Thomas Nevin & wife Ellen Shruhan seem to have had at least 6 children (so far) and there
might be at least one more but I can't see anyway to get a date, etc.
https://www.familysearch.org/ark:/61903/1:1:HQR3-HHT2Looks like an infant who died at sea/shortly after arrival? so presumably there should be its mother on board...
Added- got more on NY. relations last night before internet started acting up which I'll have to post later.