General Power of Attorney executed by NRI

Hi, My brother who is a NRI wishes to buy a property in Virar in Maharastra. He had executed a General Power of Attorney in favour of my mother on 26th May 2015. The General POA was executed on plain paper and franked for Rs. 500/- from Kapol bank in Malad and was then Notarized from a local Notary with his Rs. 25 stamps. The property agents informed me that the General POA is not valid as it was not 'Registered' at a 'Registrar' under whose jurisdiction we stay.Hence we have to wait till my brother arrives from abroad to make a deal with the seller. Now I have the below questions : 1) Is it necessary to register the General POA with 'Registrar' if was already notarized by 'Notary'? 2) Is it necessary that it should be on Rs. 500/- 'Stamp Paper' & not franking of same value? 3) Is Franked plain paper of Rs. 500/- equivalent to 'Stamp Paper' of Rs. 500/- ? 4) was it necessary to execute/sign the POA in front of 'Registrar' rather than 'Notary' ? 5) Considering the General POA was executed by my brother in favor of my mother (family), any stamp duty or other charges applicable? 6) In case if i do need to register it with 'Registrar', under which 'Registrar' should we go to considering we stay in Malad ? Any address or link will be helpful. 7) How do we go about registering without the help of 'agents' ? 8) What are the pre-requisites in registering the POA? {eg. POA in duplicate or triplicate, butter paper in between, xerox copies should be notorized, etc.} 9) What are the charges in registering the POA ? 10) What are the payment options while registering POA @ registrar? {CASH/internet banking/ DD/ etc} I hope you guys can help me out and appreciate it. - Jeff