Here's the problem: we don't know how much control they have over it. So far, it's always been passive: Sapphire made the room colder just by being there, not cause she wanted to, and Ruby burned through the carpet by accident because she was mad, and couldn't turn herself down.
So I'm gonna Support B. Temperature manipulation makes more sense than hot/cold manipulation (you can't manipulate cold) but it's the best of the three.
Kinesis/manipulation refer to being able to control whatever its being used for, in this case fire and ice, and Ruby and Sapphire have been seen to be able to control them. All we have seen is that their body naturally, seemingly out of their control, regulates temperatures to extreme level. We have not seen them controlling the elements in any way.
I'll go Neutral for B and Oppose for A and C, because, while I always choose kinesis, the terms are wrong. Cryokinesis is Ice Manipulation rather than Cold Manipulation, and Thermokinesis means that you control temperature itself, being able to raise it and lower it.