Question: What is the ruling regarding making the talbiyyah as a group in chorus?

Response:
Some of the pilgrims make the talbiyyah as a group in chorus, so one of them is either at the front, middle or behind and makes the talbiyyah whilst all of them follow him in chorus. This has not been mentioned on the authority of (any of) the companions. Rather, Anas Ibn Maalik (radhi-yallaahu 'anhu) said:

((We were with the Prophet (sal-Allaahu `alayhe wa sallam) (on the Hajj al-Wadaa' (farewell pilgrimage)) and from amongst us were those who recited "Allaahu Akbar" and those who recited "Laa ilaaha ill-Allaah" and those who reicted the talbiyyah)).

This is (what has been) legislated for the Muslims, whereby each one then makes talbiyyah on his own without joining together with others.

Shaykh Ibn 'Uthaymeen
al-Bid'u wal-Muhdathaat wa maa laa Asla lahu - Page 394;
Fiqh al-'Ibaadaat - Page 343

Taken from fatwa-online.com