Since they are mostly reasonable and have Astarions siblings to take care of them, they might actually lead a pretty decent life in the Underdark. Of course, it all could go south, but I have a hard time killing children and poor sobs like Sebastian, who begs for his life basically.
Btw, op, this is the reason, I don't play paladins - it just often don't make sense to me, what breaks the oath and what not.
