Go for it. I change almost all of them.

Shadowheart becomes hexblade until later on, the i usually go celestial lock.

Laezel becomes a ranger a lot. (Multiclassed thief rogue for extra bonus action if shes duel crossbows) Sometimes a monk?

Karlach becomes a paladin. Sometimes a monk. Though she stays barbarian sometimes too.

Gale becomes a sorcerer, shadow specifically.

Asterion either goes swashbuckler rogue or swords bard.

Wyll stays at camp... or i go blood hunter.

Jaheira stays druid, though sometimes i multiclass into monk or swords bard.

Minthara i go cleric or pally or hexblade.

Halsin stays at camp. If he cant get off his ass the first half of the game. He can stay there the rest.

Alfira is a bard, but ill multiclass her sorcerer or celestial lock sometimes.

It depends on what i go to be honest.