when matters "este" when "sunteţi"?
For example: cine este in cameră? or cine sunteţi in cameră?
"Este" is used in the 3rd person singular, so when you are talking about a single person who is not yourself and who you're not talking to directly. "Sunteți" is used in the 2nd person plural. This means either when you are talking to a group of people or to a single or multiple persons in a formal manner.
To my understanding "cine este în cameră" is correct and "cine sunteți în cameră" is not. There could be another meaning that I'm not aware of though.