بسم الله الرحمن الرحيم
If it is Hajj-e-Badal or Umrah-Badal then it may be done only on behalf of one person, not many. And if someone wants to do isal-e-sawab of his/her Hajj or Umrah then he/she may do isal-e-sawab to as many people he/she wishes from his/her Hajj and Umrah. (al-Durr al-Mukhtar & Radd al-Muhtar, Kitab al-Hajj, Bab al-Hajj An al-Ghair, 4: 28-30, pub. Maktaba Zakaria Deoband).
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.