The Mysterious Voices (which I love that they're being called various muppet names XD) are most likely either from Serini's gate itself (the oathspirit thing), IFFC's begrudging workers, or a mysterious third party.

One thing I'd like to add: look at SRD, the poison that stands out is Drow Poison. Drow Poison is an injury poison, and inflicts unconsciousness on both primary and secondary damage. I can't explain why they'd have Drow poison (they might just be high level enough that they can find some easy), but it suggests that the poison may have been meant to knock the Paladins out instead of killing them outright. They may well be against the party, but they aren't necessarily going to kill them outright.