Power of Attorney

My brother and his wife have purchased a property in Pune where they are listed as joint owners in 2010, they had issued a General Power of Attorney in my name at that time so that I could execute the purchase as they are residing in the USA. Now, he wants to sell the flat. However, the consulting lawyer asked him to make another power of attorney. My brother sent across a new power of attorney so that I can conduct the sale procedure on their behalf. 1. Is it okay if the new power of attorney is just notarized in USA and again notarized by me in India or is it mandatory for the power of attorney to be attested by the Indian Embassy in the USA? 2. Since my brother and his wife are joint owners, do we need to issue 2 power of attorney's, one for each? Does the power of attorney have to be issued in the name of a blood relation (since I am not related by blood to my sister-in-law)? 3. Is it mandatory to include the details of the property to be sold in the power of attorney or would a general power of attorney for sale issued in my name suffice?