SInce you are receiving the rents from a long time and having the authorization to receive the rent as per your statement that means as per the
NEW Tenancy Act of west Bengal ;\
"landlord" includes any person who, for the time being, is receiving, or is entitled to receive, the rent for any premises, whether on his own account or on account of, or on behalf of, or for the benefit of, any other person or as a trustee, guardian or receiver for any other person or who would so receive the rent or be entitled to receive the rent, if the premises were let to a tenant;
Now the question arises about the tenancy rihgts claimed by some distant relative of one of your tenant.
"tenant" means any person by whom or on whose account or behalf the rent of any premises is or, but for a special contract, would be payable, and includes any person continuing in possession after termination of his tenancy and, in the event of death of any tenant, also includes, for a period not exceeding five years from the date of death of such tenant or from the date of coming into force of this Act, whichever is later, his spouse, son, daughter, parent and the widow of his predeceased son, who were ordinarily living with the tenant up to the date of death of the tenant as the members of his family and were dependent on him and who do not own or occupy any residential premises, and 2 [in respect of premises let out for non-residential purpose his spouse, son, daughter and parent who were ordinarily living with the tenant up to the date of his death as members of his family, and were dependant on him or a person authorised by the tenant who is in possession of such premises] but shall not include any person against whom any decree or order for eviction has been made by a Court of competent jurisdiction: Provided that the time-limit of five years shall not apply to the spouse of the tenant who was ordinarily living with the tenant up to his death as a member of his family and was dependent on him and who does not own or occupy any residential premises,
Now if the person /occupant claiming to be the relative of the tenant can approach to court and deposit the rent with civil judge as per the new rent act.
SInce he is in occupation and he can file for protection of tenancy as he will prove that he was living with tenant till her death and he has signed the death certificate for that pupose. He has planned already to occcupy the premises and he is working as per instructions of some legal expert.
The process is time consuming in the court It is better if you can sort out the matter with him peacefully.
You can file also an eviction suit that will be same way and he will get chance to dposit the rent in court.
It is better you consult some senior lawyer in this reagrd and act sanely to protect your intrests at the best.