Document requirement for different situations are different. It is advised to consult a legal advisor.
In the face of the situation I can say you need to have
1. Sale Deed
2. ROR (may not be there if the sale deed is new)
3. Up-to-date rent receipt.
4. Legal Heir (if original owner is dead)
5. Death certificate of the owner.

Hope this will be useful.
Subhakankhi Choudhury
Architect