How is "lagh" pronounced "lee"? Come on now.
Siobhan = "Shi-vawn" Gaelic languages are not to be reasoned with.
Quick'n'dirty Gaelic Rule: if you see an "h", then whatever consonant it's next to is Absolutely Positively not going to be pronounced in a way that you will find logical. Also, you will pronounce no more than 60-75% of the letters in any given word.
and then - not Gaelic- there's the singer Sade...
And also not Gaelic, but Polish, Basia = Basha = Polish for Barbara.
My People take no responsibility for other people's wacky pronunciation rules. Our own are mostly from the Romans forcing the Celts to transliterate their existing language onto latinate letters (if I remember correctly).
Have marked Smayhem Sprog pics for later enjoyment (*grumble* work computer blocking pics *grumble*).
Much, much ~ma for your friend and his family, Corwood.