I've been browsing the McGivern genealogy sites and have just found a post on genealogy.com forum.
I come from a family which has kept a lot of the legends and stories alive and what I know is a mix of stories passed down from my grand mother (Mary Jane McGivern) to my father and then to me.I have also been continuing my fathers research on this subject now we have the internet! All his research was from family and checking the records in Belfast (which was difficult due to the post office bombings).
I am a decendent of Owen McGivern (He had two families; one Irish and one USA.I will tell you what I can.
I was born in Scotland but my family are all irish (mostly N Ireland).
I have all the brothers' birth/baptismal certs.The mother's name varies- McIntyre, McEntire and McAteer.
They were born/baptised in St Matthews, Belfast. They came from Hollywood in Belfast/Antrim. There birth years were as follows: John 1855 Arthur 1857 Antrim Owen 1859 Antrim Bernard 1862 Thomas 1863 William 1866 Patrick 1871
I also have Owen's marriage record to Mary Jane Murray in 24-Feb-1879.
From family stories I can tell you the most about Owen. He Married Mary Jane Murray and they had two children together.One did not live and the other was James Fredrick McGivern (my Great Grandfather).
It's not clear why, but as you say around the mid 1860s Owen (and apparantly all his brothers) left for the USA.
Owen ended up in CA(USA) I am assuming this is California.
He had a son and daughter there and I believe the mother's occupation was a housekeeper.
Mary Jane McGivern (Murray) - his irish wife - is listed in the 1911 census for Belfast as having been a widow since 1900.
I'm told she knew Owan was dead because a Reverend Dan M McCashin (who married her son and daughter in law in 1906)visited her to tell her Owan was ill in USA and she should go there to visit.She refused to do this on the basis that he had "done very well without [her] all this time and he [could] stay like that".
I believe he died from Consumption/TB although this is hazy.
I also remember being told either Owen or one of the other brothers died in the Bay of Biscay and that one or other of them fell off a pleasure boat and drowned (this may have been wishfull thinking on the part af my ancestors!)
I hope this message reaches you and it is helpful.I'd love to know what you know of the McGiverns and what became of them!