OP This is all really complicated. So - as the saying goes - hold on to your hat!....
Iona is a really beautiful island with a long and fascinating history. To many people it is also of spiritual importance. It would be lovely to be named after such a place; the name would be full of meaning. (Just like Sorcha has the wonderful meaning of light or brightness - and by association, hope and joy.)
Iona as a name is actually English. It came about because an English-speaking historian long ago misread some ancient documents. (In medieval latin, which looks beautiful on the page but can be difficult to decipher, the letters m and n and u and v can all look the same, so you get confusions such as Iona and Iova etc etc etc . And the latin word for island is 'insula', which is also another source of confusion). You can read all about this here: en.wikipedia.org/wiki/Iona
The Gaelic name for the island has been recorded in several different forms. Many scholars think that its original name was based on a Gaelic word for yew tree, a tree which had significance for Celtic peoples. Names based on the word yew-tree usually contain the element 'Ivo', hence the name mentioned above 'Ivova' (Ee-VOV-ah). I think that's rather pretty!
Later, people who could speak and write Gaelic used to talk and write about Iona as 'the Island of St Columba', who, of course , had founded a monastery and religious community there, and was (admirably) a great advocate of peace. In Gaelic, one possible form of the word for 'island' was simply 'I' (pronounced Eee as in 'see'). So in the Middle Ages, Iona - whatever it's original Gaelic name had been - became something like 'I Cholaim Chille' (Eee-Kolum-Killeh - Island of St Columba). In that format, 'I' simply meant 'island'.
So, when it comes to names, I think you have a choice. You can either use Iona ( modern English pronounciation Eye-OH- nah, even among locals) as a short form for 'island of St Columba' or go back to the origins of the name and choose Ivova (Ee-VOH-ah) which means 'yew tree isalnd'.
Alas, the version Ioua is really only a long-ago spelling mistake.
I am sorry this is so long and complicated. Good luck, anyway!