Now, as to the question of alignment, you are setting yourself an admirable but formidable task here! It can be done as you say, but I would feel better about your chances if the Ranger was either very Chaotic in his goodness or Neutral/Good right on the border with True Neutral on the alignment graph. It would also help if he has an astounding ability to turn a blind eye to the actions of his compatriots, or else feels some compulsion to go behind them "righting the wrongs" that they leave in their wake. Those are just two possibilities that occur to me that might justify his presence in the group, along with your already stated revenge motive. I'll be very interested to watch what's sure to be some outstanding roleplay on your part in this game. I wonder whether your ranger might be trying to do some good deeds to counteract the evil of his associates, while hoping to do so without being discovered by them, as this would spoil his ruse of being evil himself.