Hii..

Every IIT and NIT have their own rules so I would suggest you to better ask from the concerned authorities of the NIT you are applying for the documents required during admissions.

Other than this the most important document required for fee waiver students during admissions is  family annual income certificate.

I also want to inform you that the fee waiver students are exempted from the tuition fees of the respective colleges but they need to pay the The Other fees like library fees, examination fees and other fees. No student is granted 100% scholarship usually.

Hope it helps..

Best of luck..