Valgyar kinda sucks, not a very good fighter and can't wear decent armor.
Your party looks like you need a straight mage:
Edwin - great, but you have to keep your reputation at mid-level not to lose him
Nalia - underestimated spellcaster, available very early, can wear elven chain and use sword and shiel due to dual class.
Jan - Nice guy and on long term best thief in game but not the kind of mage you are looking for as he is multi-class and inllusionist.
Imoen - can be used as primary mage once you get her back
So at present I would go for Nalia and think about who is going to leave the party after Imoen's rescue
