1. You can appoint individually your mother as the Attorney or Agent through POA, as you and your mother are blood relatives, to execute the sale deed in favour of the prospective buyer, on your behalf, in the jurisdictional Sub Registrar's Office.
2. Similarly let your wife appoint individually either her father or mother or any of her siblings as the Attorney or Agent through POA, to execute the sale deed, on your wife's behalf, in the jurisdictional Sub Registrar's Office.
3. As per above, the adjudication charges will be nominal for the two POAs, when once it's received in India, after countersigned by the official of the Indian Consulate abroad, as POA would have been executed between blood relatives.
4. However if you are prepared to pay extra stamp duty towards adjudication charges, both of you can appoint your mother as Attorney or Agent through POA and for your share (1/2) of the property it will be charged nominal and for your wife's share ( other 1/2 ) in the property, it will be calculated based on the market rate of the property.
5. To avoid paying extra stamp duty, please follow as stated in (1) and (2).