I found that if you mean to kill the goblin leaders, it is best to clear the approach area of goblins first. They call for help from the goblins outside. It helps if no one is there to answer the call. This is how I dealt with the priestess; for the drow I put a damage area beneath her before ever talking to her. (Alas, Speak with Dead didn't work on her corpse.....) Only the hobgoblin had to be fought straight up.
It also helps to destroy any drums you find.
All the goblins turn hostile only after you have killed the leaders. And if you're playing through and killing the goblins don't buy anything from the goblin traders either. Their goodies will apparently still be there. Their gold, maybe not.