Since it is a relinquishment deed, it has to be registered at the sub-registrar office where the property is located.
so, the steps are
a) A relinquishment deed should first be drafted in accordance to laws with proper description of area, boundaries of property etc and
b) the persons residing in USA should sign the relinquishment deed in presence of officials of Indian Embassy.
c) Thereafter , the persons residing in USA should also give a signed special power of attorney (again signed and attested in presence of officials of Indian Embassy) and
d) the person holding power of attorney shall then register the special power of attorney before the Sub-Registrar office after payment of stamp duty and registration charges.
e) Indian embassy officials charge a nominal fee for attestation of documents. you can check the procedure for attestation in Indian embassy / consulate website.
Hope this information is useful.