Buba is right, this achievement almost always fails because people didn't think about Arka. (I achieved the achievement as a Dark Urge, so you're not allowed to kill Pandirna either)
After Sazza is dead or saved by you, Arka leaves the room with Memnos and stands near Rolan. It's best not to talk to her, if you talk to her twice she'll leave the grove and you'll find her dead near the goblin camp.
With Mol, I would say that everything is fine since she is alive. This shouldn't depend on the quest.
