Answer: The nonverbal behavior displayed by the sisters was AFFECT DISPLAY.
Explanation: Affect display in Psychology is an external display, (verbal or non-verbal display) of emotion or affection such as by facial expressions, gestures and body language, volume and tone of voice, laughing, crying, expression, or posture, whether voluntary or not.
Affect display can be real or faked. Such as a person smiling when sad to cover their sadness.
The two sisters in this example showed an example of non verbal affect display which was a HAPPY HUG.