How to Deal with Minthara and Ragzlin and Gut
Ask Gut for a little privacy. Stick three of your party members in Gut’s room in stealth while your main character asks for the audience.
While talking to Gut switch characters to one of your companions and try to kill Gut with impunity. If you can’t one shot her then try hold person or silence on her so she can’t call for help.
You can kill all of the various loose goblin groups outside of Ragzlin and Minthara’s area without alerting anyone. You can also destroy the war drums that get played when you start combat and call allies.
Then go and kill Minthara. You can do the same thing with one character starting a conversation with her to make a sneak attack easier to position for. She also has a war drum in her room, so make sure to destroy it immediately.
Ragzlin’s a little harder, and when he goes down all of the goblins will turn on you. The easiest way to beat him in my opinion is to cast crown of madness on him so he destroys his buddies while you take out the rest of his group.
Then finish him off. You can put archers and mages in the rafters to give them height advantage and keep them out of harm’s way if necessary.