Hi
1) The POA issued by the deceased person is no longer valid.
2) Once the person has died, then the POA also expires.
3) Power of Attorney is a Delegated authority.
4) In the eyes of Law, the dead person cannot delegate his responsibilities. So the POA is invalid.
5) You should buy the property from the legal heirs of the deceased person.
6) The revenue authorities will issue the legal heir certificate to the legal heirs of the deceased person and you should call upon the legal heirs to execute the Sale deed in absence of will , gift etc.
7) Also if the property value is greater than 10 lakhs, ask your advocate to issue notices in 2 leading news paper ( 1 English and 1 malayalam) about your intention to buy the said property and ask for legal heirs to come forward stake their claim (in case they have any will or gift or interest or any minor interest in the property) so that in the eyes of law, you had made all the necessary due diligence before buying the property.
Hope this helps.