Laezel and Astarion could reclass to any martial class really.
Laezel wants to be a githyanki knight which would be a high end eldrich knight, however her story seems to be trending words breaking with gith culture so it might not make sense late on.
Astarion again can fit anything. If you give him the necromancy of thay, going arcane trigger or even just full on reclassing him to wizard might be good.
Let's make Shadowheart a Paladin.
Shadowheart's entire origin story is intrinsically tied to her being a Cleric of Shar so if you respec her into a paladin then her entire story will no longer make sense.
Shadowheart, Will, and Gale at least you should never respec into other classes. Though in general, respecing origin characters is a bad idea. If you want a Paladin in the party and you don't want to play one yourself you could recruit Minthara.
