That bank was stolen from Vivaldi in the first place. The government just confiscated a bank that had been in his family for generations, not because he's done anything wrong, not because the bank has been mis-managed, but solely because he's a dwarf. Case it! Hell, I'll HELP them steal the damned thing back!
And if you listen to Yaevinn when you help him, part of what they take at the bank is paperwork that they believe will help him get the bank returned to Vivaldi.
The Order IS evil in Murky Waters. Siegfried wasn't there, though. He might have done the same thing if he WERE there -- he does seem to hate non-humans just as much as the other members of the Order -- but it's possible that he'd have been more reasonable if he'd been on the spot. ›››
I believe it's said that the order to invade the village and assassinate the elves came from Siegfried; presumably it was either pre-planned or brought in by messenger. White Rayla is furious over it, though she may be more upset with Siegfried pulling rank on her than with the action itself.
If you side with the Order, there's a charming scene where White Rayla catches up with Siegfried and chews him out up one side and down the other (though it's not for this incident). Siegfried is shocked by her language; Rayla ignores him and keeps up the stream of four-letter words.
Siegfried is neither foolish nor evil, in my opinion; he's just unable to see beyond the way the Order has done things ever since they came to power.