My father was born in Seefin - Michael J Flynn ~ 1896 and was baptised in the Catholic Church in Crossboyne.
He had to leave Ireland "in a hurry" after the Civil War in 1925 and settled in Newton, Masachusetts, where his uncle and sister lived.
When I was a child, I remember visiting my parents' friends - the Martin Mullahey's of Watertown,Masachusetts.... in the 1940's. I'm guessing this Martin Mullahey was one of your relatives as the Townland of Seefin was only 508 acres in the Barony of Clanmorris, Civil Parish of Crossboyne, in Mayo.
I had the opportunity to visit Sefin and my father's homestead - farm - 1n 1999 with two of my Irish cousins.