spell questions: Breath of Winter, Communion M/S

[Zooko]

Is there any point in Niefel Jarls casting Breath of Winter, or do they already have all the cold aura that they can get? (I guess there must be a benefit from doing it or else they would refuse to do so.)

If I Mind Burn my enemy Communion Master, will it also damage the slaves?

Or to put it another way -- my enemy has got way too many communion spell casters and I'm trying to figure out which spells my spell casters should try to counter them.

Mind Burn is negated by magic resistance, but maybe if I give my Mind Burner lots of Astral Pearls...?

Thanks!