Hi Varun,
Perfect.... Just In Time
You must attach the Letters for Passport Request + VAC Consent Letter + pay VFS fees+ Authorized Representative letter (if required)..... you can submit the passports either at the New Delhi CVAC or at Bangalore VAC
So if you submit the passports at Bangalore VFS, the stamping will be done by the Bangalore Consulate.... it will not be sent to the New Delhi Visa Office for stamping.
I had suggested submitting their passports to the New Delhi VFS because I thought your parents are in New Delhi currently.
For submitting the passports:
Either your dad or your mom or your sister can submit the passports for all three persons if they visit the VFS Office between 9am-12pm
After 12pm, your mom + dad + sister will be required to be present personally to submit their individual passports.
You can ring VFS to reconfirm this.
Also, you can choose to collect the processed passports personally from the VFS Office later. I think if you opt for courier to the Kerala residence then it will delay matters by 1-2 days
Do keep us posted