kinda new plz help with 2 question

Hey im new to BG series and got a couple questions that might be stupid. I've got the mage d'arneise or whatever in my group and at first she will cast spells but now all of a sudden they are red and uncastable? why is this? another why is it that when I try to kill the guy who killed anomens sister my entire group leaves cause they are pissed off ? what are they mad about? and also where do I get potions to kill trolls??

THANKS IN ADVANCE

[omegadawn]

Is Nalia wearing armor? She can't cast while wearing armor (dual/multi class mages cant) . Also if your reputaions falls under 2 or 3 good characters will leave your party, so killing that guy must have ruined your rep. Kill trolls with fire or acid. you can use spells or fire/acid arrows.

[Ladyzekke]

Right, Nalia can't wear armor and cast spells, try to find a robe, she can wear that and cast spells. With the Anomen's sister quest, since you never really have actual proof as to who really killed her (all you have to go on is the drunk father's rumors), the only thing for Anomen, as a "Radiant Heart", to do is to let it go. If there is some way to find the proof, you could THEN go kill the guy and your rep won't go down, but I never found any myself.

SPOILER
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If you kill him, then Anomen will not be accepted into the Radiant Heart later on and he will become Chaotic Neutral and even more neurotic. He will turn on your party at the slightest provocation too. Get him to report the incident to the authorities instead and assuming no other transgressions, he will become a knight later on and gain in Wisdom and his Ego will double(unfortunately).