The current companions are our grey-to-red set. I think it's unlikely that you'll 'corrupt' them too far, given that they are already the representatives for our dark side. Looking at the calssical defintions, and bearing in mind that evil is defined by selfishness more than anything else:
Lae'zel is our representative for Lawful Evil, and doesn't need too much explanation on that score. She is the classical definition of this stance.
Astarion is our representative for Chaotic Evil: he's in it for himself, and himself alone, and he doesn't care who gets hurt in the process - even relishes it, and his only guiding code is "What Astarion thinks will be the most fun"
Shadowheart (Shar Following) is our representative for Neutral Evil: while she is busy being a worshipper of Shar, Shadow is the classical embodiment of neutral evil; she is ultimately selfish, and puts her own personal needs and wants ahead of everything else as being of supreme importance. Other people are useful only in as far as they are useful to her, and she will absolutely not put herself in danger for the sake of others, unless she feels she has no other choice... at the same time, she isn't directly vindictive or bloodthirsty, and she prefers, if there is no difference to her, to avoid unnecessary bloodshed. Shadowheart seems slated to have an alternate path where she returns to Selune, or something to that extent - and it's from here that her good-aligned affectations and facets seem to surface. That version of shadow would likely be neutral good.
Wyll is our representation of Chaotic Neutral: He follows his own code, believes in doing what he thinks needs to be done, regardless of any other systems or structures in place. He tries to be heroic, and wants to be, and to be seen as, a good person, but he isn't there yet, and he has a lot of background baggage. He's driven by a need for vengeance and for personal reasons, even though he wants to be seen to be acting for the greater good. Indeed, he prefers to act for the greater good, when he can, but... if he is forced to choose between what would be considered the "good" action, and his personal revenge, he'll probably slip... so Chaotic Neutral, for now.
Gale is our representative for true neutral: He moves and acts within the world, according to his own plans and designs. he would generally choose to help someone rather than not, so long as it doesn't inconvenience him or his plans too much, and he is considerate of others around him, but unless there is a very good reason for it, he generally won't suggest putting himself in danger. He likes to see his friends succeed, and likes to have friends, but he never stops assessing his friends and companions for their strengths and usefulness - he doesn't do it maliciously, just pragmatically. Perpetrating overt evil in front of him pushes Gale more strongly towards good in response, so True Neutral, but leaning towards good, or at least a desire to be so.
Really loved you summarisation of the characters.
Thank you for it.
