I'm also having this exact problem, basically every detail. Seeker chosen, I pass the Religion, Metaphysics, Diplomacy checks to where both Seeker and Survivor won't initiate a real conversation and just say 'go end this', then no matter how I go through these dialogue trees with Slayer, despite passing the 22 Intimidate check he will attack and Seeker will join in shortly after.
I do have a few mods installed, a UI mod to add colors / icons to afflictions and such, and a mod that lets multiclass characters get to power 9.
Party is Watcher (Skald / Soulblade), Konstanten (Barbarian), Pallegina (Paladin), Xoti (Priest), Aloth (Wizard), in case any of that would matter for some reason.
