attack dallis or vredeman until they're around 20% hp and the fight will progress
it's an extremely annoying bug as you miss out on a whole part of the finale (although i guess not really if you chose to give your source away)
it's never happened to me with ifan, but it did happen to me with fane; i chose to fight them, then the fight doesn't trigger and everyone just stands around indefinitely. my guess is it has something to do with having companions with specific endgame dialogue in your party
this absolutely needs to be fixed asap