... and freshly defragged.
Fiolar, I'm sure you'd agree that when we're talking about an unstressed syllable, giving a phonetic representation that's valid from Vancouver to Germany is a tricky business. Maybe the difference between our respective pronunciations isn't as acute as it might seem in writing, or maybe it's because my most influential Irish teacher was a Kerryman. But I would certainly proniµounce "ionad" as "UN-nad", not "INN-ad", and I would colour the neutral or centre vowel of Siobhán with an "a" rather than an "i".
Dicho, I know they say Guinness doesn't travel well, but I'm appalled at what you tell us people are apparently doing to the name. The first syllable is stressed, and sounds like the "gin" in "begin". The second syllable is unstressed and has a "neutral" vowel. You could say "Begin us" and then just leave out the "be".
Seana and Seona are, as far as I know, modern attempts (my guess is late 1970s) at a feminine version of Seán - or else they may come from Scotland.