1. Only NOC issued by your US Citizen brother will not help.
2. He shall have to register a gift deed gifting his 50% share of parental property in your favour by paying the required stamp duty which will be 1/2 % of the Circle Price of the said property since you are his blood relative.
3. The related Gift Deed prepared by your Indian lawyer sent to him can be signed and registered by him before the appropriate officer of the local Indian Consulate, in case he is not in a position to visit the registrar in India.
4. Some consulate might refuse such registration due to ignorance of law which he shall have to explain to them appropriately.
5. While registering the gift deed in your favour, he will require the legal heir certificate to be issued by your ward commissioner of the Kolkata Municipal Corporation.
6. If he fails to get the gift deed registered at USA before the Indian consulate then he shall have to visit India for registering the same before the Registrar.