Fiolar, are you sure Sam Hain isn't Peter's evil brother?
One of the problems with suggesting Irish pronunciations is to get an "English" transcription which works on both sides of the Atlantic (and which is sensitive to the fact that there's more than one "American accent"). Another is variations between dialects of Irish.
For Siobhán, having learnt Munster Irish throughout my schooling, I would suggest "Shove-AWN".
But a Donegal person would probably suggest something like "SHIV-enn".
One of the things that amuse but also mildly irritate me is the fact that some people in the US go as far as to adopt the spelling Caitlin(n) for their daughters, but then pronounce it as if it were KATE-linn, whereas the Irish pronunciation is almost indistinguishable from the usual English pronunciation of "Kathleen". It almost seems like protesting their Irishness too much.