Hi Bess, Pryvit!
Yes, but TalkIrish is all about respect for smaller cultures and languages, so looking up a bit of Ukrainian just seems like the natural thing to do (and I'm always happy to learn a couple of words of another language!)
Anyway, to answer the question about names, the word "an" is the definite article, so Shee an Gannon means the Fairy (or Fairy-mound, could be either) of the Gannon (which might be a place-name). I don't know what the original of the word Gannon is - it certainly isn't an Irish spelling.
Tuath Dé Danann is from the ancient Irish Book of Invasions. It means "The People of the Goddess Danu". Dé is related to the word Dia, which means God.
Fionn Mac Cumhaill was the hero of many Irish tales and this is anglicised lots of ways: as Fin M'Coul, or as Finn McCool, or as Fingal (as in Fingal's Cave).
Knockmany is an anglicised version of Cnoc mBáine and is in Tyrone. Cape Clear is Oileán Chléire in Irish and it is in Cork. I have never heard of Knockgrafton but again it is an anglicised version of some Irish original (or perhaps just a fictional name).
Andrew Coffey is an ordinary English version of an Irish name. In Irish it would be Aindriú Ó Cofaigh or Aindriú Ó Cobhthaigh (in modern and older spelling). Coffey is a common name in Cork (some of my relatives were called Coffey) and also quite common among the Irish travelling people.
King Hugh Curucha of Tir Conal apparently stands for Aodh Crochta (Hanged Hugh) and the Tir Conal is Tír Chonaill (the land of Conall) in the modern spelling, which is Donegal in the north west of Ireland.
Hope that's OK. By the way, your English is really good - you'll have to learn Irish next! All the best and Щасти вам! Seán.