My brother is a tenant in Chennai and has been living in the rented house since August 2010. Since the landlord is in the US, the brother in law of the landlord had created a contract for the first year and signed on the agreement on a Rs 20 stamp paper on behalf of the landlord. I dont think there is any authorisation letter or power of attorney given to him by the landlord.

In the second year the landlord's wife who I believe does also not have  power of attorney from her husband has signed the agreement on his behalf again on a Rs 20 Stamp paper. Is she suthorised to sign on her husband's behalf if she is not a joint owner of the house?

ALso if agreement is made on stamp paper only then is such an agreement having any legal validity at all?