There was someone in Rhea's team who recognized Eren as soon as he was hit with the latter's soul sense.
He had followed the developments in Edin closely and was up to date with Eren's identity. Among all the rising heroes of Edinburgh who came into the limelight after the battle of Edinnica Arena, Eren left a deep impression on people. After all, Grimdawn was praised by King Emil himself and bestowed with a memorable title.
This man wanted to let Rhea know she was about to clash with a bona fide titleholder. But Eren's soul sense made him incapable of voicing his thoughts. No voice came from his mouth even when he opened his mouth to speak.
"You all stay behind as well," Rhea commanded firmly, her gaze fixed on Eren. "Let the leaders of our teams negotiate and find common ground."