Welsh doesn't have the schwa sound for unstressed syllables like English does (i.e.,
Shannon,
Shannen, Shannin & Shannyn would all pretty much be pronounced the same in English), so
Eirwen would be pronounced /EYE'r wen/ or /AYR wen/ with the second syllable like "wen" and not "win." Also, the "r" is rolled in Welsh.