Whether the Ration card NEREGA Card etc can be accepted as Valid Proof of Identity/Address for the family members listed in the document in case they do not have separate PoI or PoA document?

Yes. The family entitlement documents is accepted as proof of Identity/Address for family enrolments as long as the head of the family whose photograph appears on the documents presents and verifies the identity and address of the family members and the Registrar authorized verifier countersigns the copy of the document as proof of acknowledgement.