It is possible - with Durges background it is clear (and please only read this, if you don't care about spoilers),
that they are Bhaals essence and basically his puppet until the tadpole gave them free will - similar to Astarion and Cazador actually. Withers/Jergal will tell you so, when you resist in act 3 and he has to step in to save you. He tells you, that you now will be able to live free from your fathers/master clutches and can finally do, what you want. And if you play Durge as a good character, then that is, what your character would have been without Bhaals influence over you.
This doesn't change much for me, tbh, considering a certain event happens only after they get tadpoled. And well, DU gets away with it, because none of the companions care, not even the good ones. Also, I'd have to metagme and reload some other events, which are optional, but I have not managed always to avoid them.
