Thank you, I'm glad that you enjoyed the game! : D
Yes, doppelgangers have different dialogs, and there are certain visual cues that indicate who's a doppelganger. They get randomized on day 1, just before you collect rent. There's a minimum of 5 doppelgangers per game (someone even got 11 doppelgangers in the final results and just 1 human tenant)