Peter
I am the eldest son of JOHN DUFFY,
who was the eldest son of JOHN JAMES DUFFY,
who was the eldest son of JOSEPH DUFFY,
who was the eldest son of JOHN DUFFY,
who, I thought, was the eldest son of EDWARD DUFFY.
Now you've gone and spoiled it.

It appears that EDWARD and ELIZABETH came from Ireland to Liverpool, then sailed to America, where John was born, then sailed back to Liverpool, where the rest of the family were born.
By 1851, apart from JAMES and JOHN, the family have disappeared once more.
Brian