For the encounter at Lae'zel, you are perfectly capable of attacking the Tieflings right away, so I see no problem there.
Before entering the grove, you see that humans seek help of the so-called devils. I think that's enough to allow a character to think I may just as well talk to these people before I cut their throats.
(Actually, this makes me want to check out what happens if you try to side with the Goblins during the initial grove attack. Will the Golbins stay hostile? But this is degressing from the topic, sorry)
