Delwaer can only be found in the dining room if Oskar Fevras was never rescued from Brem in Act One. He can be seen arguing with Sir Gorran Penghyst about a painting he sold, which Gorran claims is a counterfeit. Delwaer believes Gorran should have known it was a fake, while Gorran believes he should not have sold a fake in the first place.
If not intervening, the pair agrees to duel and heads out to a balcony. Combat starts between the two and only ends once one of them is dead.
The party can intervene to stop the duel:
[INTIMIDATION] Stop this, or I'm sticking both of your heads through that bloody painting. (DC 18)+1+1+1+1+1+1
[PERSUASION] Why not just sell the fake to another gullible fool? (DC 18)+1+1
[OATH OF DEVOTION] Do not sacrifice your lives on such petty grounds. They are too precious.+1+1
Or, the party can let the events play out:
Sounds like a duel is the only answer.
[HALF-ORC] This can't be solved with words - only blades. Fight! WIN!+1+1+1+1+1+1
[FIGHTER] You are clearly novices, but I will serve as second for you both, if you wish.+1+1+1+1+1+1
[OATH OF VENGEANCE] Such actions demand retribution. It is only right you deliver it.
[OATH OF VENGEANCE] Sounds like a duel is the only answer.
Or, if failing a check, the party can also attack them both.
If Oskar Fevras is rescued, the manor is haunted and the art exhibition does not happen.