1. the cousin can at best be considered as a caretaker of the land
2. the owner can require the caretaker to anytime vacate the land
3. the cousin can claim that he is a lessee or tenant of the land and thus try to retain his possession, but this needs to be denied by your relatives. Also the cousin needs to proof to show that he paid rent in order to claim tenancy or leasehold rights
4. best stand would be that the cousin is merely a caretaker and ought to vacate. There are supreme court judgments stating that caretakers have no right in the property despite their long possession, when the owner calls upon him to vacate the property
5. first try and talk to the cousin and ask him to move out
6. if he does not relent then issue a legal notice
7. when the notice period stated in the legal notice expires the cousin will be considered as trespasser and then you can file a criminal complaint against him with police
8. a separate civil suit for eviction and possession and for injunctive reliefs can also be filed
9. no POA should be given to any person. As it is as per the SC ruling no property can be sold or transferred through a POA. But nevertheless it would be safe to not give any POA to any person for the same may be misused
10. its advisable to do the sale deal in person or through a trusted family person only