Tenant not evicting the house even after expiry of rent agreement

We have given our house situated in south Delhi to tenants in 2013 with 11 months rent agreement and we further renewed such agreement in 2014 and 2015 and after expiry of agreement in may 2016 we asked them to vacate the house as they never paid us rent on time and also defaulted in payment of rent in February 2015 , so they agreed to leave and asked 1 month time to vacate but they didn't leave even after expiry of 1 month and asked us 4 months more time so we gave them 4 months time on condition that they have to give us in writing that they will vacate after 4 months and they gave us in writing that they will vacate in 4 months but even after expiry of 1 month they again asked us 1 month time as their financial condition was very poor and they were not able to finance the shifting cost and also to pay us Balance due so we again gave them one month time but now also they are not vacating the house and they have also not paid us rent from last 2 months so we want them to evict now . So I have certain questions in this regards:- 1. How much maximum time it may take in court to evict them if we approach to court? 2. What will be the estimated cost for the whole case if we take it to the Delhi district court? 3. Guide us step by step what shall we do now? How could we approach court and lawyer? 4.do we need to give a formal notice first of 1 month asking them to vacate this house before suing them in court?if yes shall we need to send it through lawyer? If yes how much(estimate) it will cost to send legal notice to tenants ??? Thanks in advance