Tennent not vacating the house

We rented our home to a tennent on July 1, 2017. The tennent got a rent agreement drafted for 24 months and convinced my parents at the time that it is just a formality - he will vacate the house in 11 months if need be. Since he was referred by a friend, my parents did not mind signing the agreement. Now, the situation has changed a bit and my parents want to go back to that home and live there. My father asked the tennent to vacate the home in June but he did not do so. Upon asking further, he is now threatening to send legal notices and not responding to any communications. He has not even paid the rent for the month of August. The rent agreement is very one-sided and does not specify any process for the owner to ask the tennent to vacate the house. It does however mention that the rent is to be paid on 1st of every month. The tennent has violated this clause. Can we consider the rent agreement null and void due to his failure of payment of rent and ask him to legally vacate now? Thanks a lot for your advice.