A lot of what happens surrounding the Ivalice raid is deliberately left vague; such is Yasumi Matsuno's particular idiom.

Voidsent aren't all auracite-mutated people, though some are. Most are just what remained of normal people after the Flood of Darkness twisted the Thirteenth.

We don't have any information on the Sin Eaters at present. The fact Innocence is the implicit model for Admadpor's Kuribu raises a lot of questions...