Power of attorny

I am planning to buy a Property in Navi Mumbai the owner of this property is a friend of mine who is staying in USA, he is ready to sell this property to me but I am facing a problem in Executing the agrement as he is not in town. The owner is read to give a power of attorney to his sistr in law who is here in bombay, but we are unaware of the procedure of how to get a POA if he is in the USA ??? Is there any way i can get this transaction done please suggest...