Evicting a tenant

Hi, My parent have a property in bangalore which they have rented to tenants. There are 3 tenants in total out of which 2 tenants are creating an issue. One tenant is living for the last 3 years, We had made an agreement for the 1st year but no agreement is in place for the last 2 yrs. Since past 7-8 months they have not paid rent. They have partly vacated the house 2 months back but not given us the key as they are asking for return of advance amount first. We even agreed to give them the remaining advance but they want more advance they what is to be given. What can we do in this case?? The other tenant is living for the past 1 yr. We had made an agreement and given them to sign but we missed out taking a signed copy back of the agreement. They paid the rent for the first 2-3 months but have not paid rent since then. The advance they had given has been cancelled out since they have not paid rent for the last 7-8 months. In fact they owe us 2 months rent but yet they are not paying nor vacating. Everytime since last 2 months they assure that they will vacate in the next 10 days but they have been false assurances. Please suggest what to do?? What will be the overall cost if we take the legal way and how much time will this take? We live in Mumbai and my parents are Senior citizens and this is their source of income since they are retired. They dont have the time and health to keep on following on this so kindly suggest the course of action.