Poa of nri to sell property in india

Buying NRI property through PoA, registered in India Hello, I have identified one property. The owners ( Husband and wife ) both are NRI's and settled abroad.The wife has given poa to her sister residing in India and husband has given poa to his sister-in-law ....means his wife's sister.Same has been adjucated and adequately stamped in India. PoA contains all rights of registration and execution. The owners are saying that they will discussed with lawyers about their intention to sell the property in near future and accordingly PoA has been prepared. When I submitted the file along with PoA to Bank for loan, Bank is taking objection to PoA by saying that, wife ( the co-owner of the property ) can give her rights to her sister but the husband cannot give poa to his sister-in-law .He can give the rights only to any relative in blood relation ( her father, mother or brother/sister ). Hence, Bank is asking me ask the co-owner to execute one more PoA in favour of his blood relatives. Also, Bank is saying that, there is every chance that Registrar / Sub-registrar might take objection at the time of registering the property in my name. I would like to know, whether the objections raised by Bank is valid.Also if this poa has to be excepted what amount of stamp duty has to be paid,is it equivalent to the amount of stampduty to be paid for registration of the property....which is 6% in Maharashtra. Kindly guide me. This is bit urgent.