What you have also clarified son John's birthday and another first born son. Please check to see if you have death records for Michael. He never immigrated to the US with the family.
I don't believe there are any relevant death records. The parish did keep a death register, but that ended in 1841, before the time of interest, while civil registration did not start until 1864.
As regards US immigration records - have you noticed that the record you have for John is before the birth of Margaret in Ireland in 1849? Now it is perfectly possible that he went to the US first, on how own, and brought the rest of the family over later - but if so, is there an immigration record for the wife and children? Or is it possible it is the wrong John Melville?