Hi there and thanks for looking at my post.

George was born in 1866. Siblings as follows:-
Daniel Sullivan (1854) - may ancestor. Never left Ireland
Denis Sullivan (1842)- emigrated to US. Found a *possible* match on ancestry but not sure
John Sullivan (1854) Believe went to US. Nothing known
Catherine Sullivan (1857-1915) Stayed in Ireland I think. Married a Tom Gill
Jim Sullivan (1860)- emigrated to Australia. Know he married and had at least 2 daughters but no other info known
Nora Sullivan (1862) - moved to US and married Frederick Schreiner. I have seen the tree you mention on Ancestry but have had no reply from tree owner to try and verify the link but seems likely.
Mary O'Sullivan (1864-1951)- Emigrated to US and married Jim Gill. Lived in Montana. Am in touch with a descendant of this couple.

An old letter i have mentions George as an accomplished musician and accordion player and am intrigued to try and find some trace of him as my late Godfather shared his name.

Any help appreciated!