Add family members as following and book slots for them:
• Click on 'Book Vaccination Slot' -> '+Add Member' or Go to 'My Accounts' -> 'Manage Family Members'
• Add details of your family member
• Click 'Book Vaccination Slot' - > Select your family member name (selected member is highlighted in green)
• Select the slot as per your requirement and complete the booking
If you are trying to book Corporate sponsored vaccination slot, you will be able to book vaccination slots for your family members only if allowed by your company.