A lot of us here have gotten pretty good at Gaelic pronunciation, though we (for the most part) can't speak it. The combination "si" makes an "sh" sound.
An "is" also often makes an "sh" sound. "Bh" makes a soft "v" sound. Therefore, the names
Siobhan and
Aisling would be pronounced shi-VAHN and ASH-ling. The letter "e" is often pronounced "uh" when at the end of names (
Aoife = EE-fuh). Now, I'm no expert, so anybody here who can actually speak Gaelic is welcome to correct me, but I think those are pretty basic rules that I picked up from years of looking at the names.