It’s a bunch of little things, probably nothing anyone other than Feiyn or Ro would notice. Tev smiling briefly, or touching them, or showing empathy where he normally wouldn’t. Its probably a bit faster than either of them doing it alone but Tev was in the Scourge for almost a decade, and really didn’t have much of a reason to change for a good long while after that, so its isn’t really a quick process to do what is essentially un-brainwashing him.