I admit it's not as obvious as I intended it. It's not brute force since there is the correspondence between the magic word and their meaning. I'll make sure the objective is more clear, but for a walkthrough:
1) One of the girls says they're freezing, the answer to that is Fire -> More -> For a day
2) This one needs more hints, I'll fix that in dialogue, but basically you don't care about what they ask, and like the others in the camp you can make their Lips bigger, then tits. Lips -> More -> Forever.
3) The last one requires 2 steps, and as indicated, you need to alter the mind first. Mind -> Stop -> Forever -> Chest -> Bigger -> Forever.
Let me know in hindsight which hints you'd have wanted to be more obvious! Thanks for the feedback!