NRI legal heir Signature on bank affidavits for closure of deceased deposit accounts

Respected Sir/Madam, My father died recently and myself, my mother and my sister are the legal heirs. I have got the death certificates and legal heir certificates as well. My sister is an NRI working in USA. There a a couple of bank accounts of my father without a nominee and the banks are requesting for a NOC letter and Disclaimer (On stamp paper/green sheet) signed by myself and my sister and Notorised to settle all the deposits to our mother. Since my sister is NRI, they mentioned that she either needs to come in person or the documents be sent to USA for her to sign and return back with some certificate from the Indian embassy. Should I first get the documents and forms signed by myself, my mother and witnesses before a Notory and then send it to the USA for my sister to get them signed and certified by Embassy? Or Indian Notory can only notorise only after the signature and certification by Indian Embassy/Consulate in USA? Can you advice in detail step by step for the above procedure to get my sister's signature on the affidavits and forms/letters? Thank you