So I enter Raedric's hold via vines, got to the sanctuary and disguised my team in Berath's robes. All good so far. I found Nedmar and through choosing all diplomatic options he gave me a secret passcode "that would do me much better than any disguise". Awesome, apparently I can go back to normal armor since I know the passcode. I MADE A FEW STEPS AND THE WHOLE FLOOR TURNS HOSTILE AND KILLS MY PARTY.
O N T R I A L S O F I R O N
That was like, the 30h hour of gameplay...
Thank you Obsidian for such misleading dialogs. Too bad I can't refund it now...