Anyone who tries to kill you is your enemy ... Yet you agreed to travel with Astarion, even if your first encounter with him started with knife on your throat? Odd ...
That is the thing with Gut ... She played her cards, and lost ... she didnt want to aly with you, she wanted to exploit you ... she failed. That is what evil characters usualy do.
As for other goblin leaders ... they both see themselves on top of foodchain ... you either proove them right, or wrong ... depend of your own character motivations ... Anyway they have no reason to bargain with you ... you either obey, or kill them ... anything else would be out of role.
As for intelligence ... feel free to think im wrong, but taken what things is tied to intelligence rolls, that stat should be more like named knowlege.