For the Bhaalists with Sanctuary, use AoE spells or bombs. AoE hits people with Sanctuary too.
Just make sure to not hit the hostage or have a wizard with Evocation.
The magic missiles are a good advice, combine that with a Haste spell or potion to be able to cast even more MM.
You can get an amulet in the Underdark from Blurg or Omeluum ( don't remember) , that strengthen your MM and gives the spell to the wearer. So you theoretically could equip a non magic user with it to get Unstoppable quicker dispelled.
Hold Monster or Otto's Irresistible Dance works for Orin to keep her occupied, if you want to deal with the mobs first.
A Guardian of Faith at a choke point is great advice.
As Durge, you only have to deal with Orin, her followers won't attack you afterwards.
