Brother Against Brother requires you to wait two days until the trial begins in Roa Dyr. If you go there before that time and talk to Llaren Ilvi, he will still have the trial dialogue. If you choose "Let me persuade him to repent" the journal will update and the two brothers and other needed characters will never be moved to the Hall of Judgement. This prevents the quest from being completed.

The dialogue for Llaren Ilvi should have the conditions changed so he will only have the topic after being moved inside the Hall of Judgement.