Tenant issue

Good Morning, We been facing one issue from years now. My father own a property in Chandigarh (UT). He agreed to give garage area for rent to one of his known without any legal agreement in year 2000 (17 year now). From couple years, we been requesting them to leave the place and they are very reluctant to do so. What would be the consequences if, we go legal? We do not want any headache? Waiting for your reply Regards