I agree with fylimar, Astarion comes off as chaotic evil, to use the D&D alignment terms. With an evil PC is is actually quite noticeable; I guess he isn't hiding his nature then. Also, he is the only companions that has a personal interest in keeping the tadpole, so I suspect if the absolute offers him a good deal he will take it (and stab the PC in the back on the way). Same as Gale and
Raphael, that is another potential betrayal I'd expect if you don't play along with Gale's demands.
That said, I think every origin character will be written with a potential evil & good path in their origin story. Otherwise playing them would make little sense; if the player consistently makes good choices, the story needs to reflect that, regardless who they are playing as.
I agree about Gale, given by the conversation with him after that encounter.
"We are all stories in the end. Just make it a good one."
