1. You cannot force the landlord to execute the rental agreement, if you are not comfortable or if the situation is beyond tolerance, you may vacate the premises and look for a different location.
How do you pay the rental amount, by cash or cheque, if you are paying it by cheque, then the evidence of the bank statement will be sufficient to prove that for paying house rent to claim HRA concessions.
2. You cannot force him, alternately you may either pay the rent to his bank account directly or to deposit the rent in the court every month, which shall be used as evidence for the payment of monthly rental amount for the purpose of income tax exemptions.