The spelling is probably just the mother being creative.
As your dentist says, E'Syious is very likely a respelling of Isaias
, the Spanish form of Isaiah
. The mother heard Isaias
but had no idea how it was spelled, so she invented her own spelling. The "E'" is her way of spelling the name so that people in the African-American community will pronounce it with the "ee" sound at the start. If the spelling was Esyious, many people would use the short "e" sound as in Esther
, but the "E'" makes it more likely that the pronuciation the mother wanted will be used. That's all it's "for": a creative way to get people to pronounce the name with the vowel sound she wanted.
Unless you can communicate with the mother and ask her yourself, that's probably the best theory.
P.S. It's interesting this should come up today, as it was only a few days ago that the World Meterological Organization chose Isaias
as the replacement for Ike
on the 2014 list of Atlantic hurricane names. :)