A single cow/camel can be on the behalf of 7 persons only:

Sacrifice of a camel or cow on the behalf of 7 persons is permissible.  There is a Hadith given in Sunan Abu Dawood:

It is narrated on the authority of Jabir bin Abdullah (May Allah be well pleased with him) that the Holy Prophet (Sallallahu alaihi wa sallam) said: A cow is on the behalf of 7 persons and a camel is on the behalf of 7 persons.  (Sunan Abu Dawood, Hadith No. 2810)

A goat, ram or sheep can be on the behalf of one person only.  In buffalo, cow and camel, one animal is on the behalf of 7 persons .i.e. 7 persons can participate in the sacrifice of one cow, buffalo or camel.  As mentioned in Fatawa A’alamgiri:

 (Fatawa A’alamgiri, Vol. 5 Pg no. 297)

Author: Mufti Hafidh Syed Ziauddin Naqshbandi Qadri,
Professor, Islamic Law, Jamia Nizamia.