Siobhan is pronounced shivAWN or shuh VAWN in some parts of Ireland and shoowawn (with equal stress on the syllables) in others.
Samhain (pronounced SOWunn) is one of the festivals of turning seasons; it's the one celebrated on the date when Christians celebrate Hallowe'en (All Hallows' Eve). It has nothing to do with the name Siobhan.
I don't know of any meaning for the name Siobhan, though there may be one.
Aisling is pronounced ASHling, and means a dream, or a vision, really; there's an eighteenth-century poetic form called the Aisling poem which celebrates Ireland as a beautiful young woman waiting for Bonnie Prince Charlie, under various guises, to come and rescue her; some hope, he was off burying himself in a keg of whiskey somewhere.
Ashtray is a very nice name for a child. Maybe with Gauloise and Sobranie as middle names?