I recently tried starting a new campaign with my friend. We each wanted to play our favourite characters. Mine being Karlach and hers being Wyl. When we went to do so it locked the other out of the other character. I really wish this wasn't the case. I understand it may be because Wyl's quest has him hunt down Karlach. I feel like maybe they could put in the journal that Karlach helped him off the Nautoloid so he decides not to do it and it causes your first long rest to play the Mizora punishment scene. It just seems really disappointing to lock out a character combination like this in multiplayer especially if one manages to find a 4-person group to play with because it forces you out of an option. I hope in the future they make some kind of change to how this works.