Builder Harrasment

Dear Sir, My parents are a government employees & got retired & purchased one 50 gaj plot in Burari,Delhi last two years back. Last year February 2015 my parents gave collaboration work to one builder & it was decided that he(builder) gave possession to us on February 2016 but he fail, after forcing him several times we finally got our home (not prepared thoroughly) on 8th April 2016. When we enter in home we found that nothing was in its ok condition as when my father closed the bathroom door, handle has been brooked, When my mother goes to fix nail in side wall for hanging of wall clock then found that wall brooked by corners itself. A few days back weather was not ok & heavy wind flow, one of the balcony door closed by itself suddenly door frame loose by itself. We have four floor property description is, Parking,Upper Ground, First, Second & Third. Third floor is for builder as collaboration & on the same time last year when we gave collaboration work we purchased Second floor @ Rs.17 lakhs & taken loan of Rs.8lakh from him & EMI of Rs.30,000 per month for three years, starting from December 2015. My mother continuously paying the EMI on time & no one cheque has been bounced, but still he (Builder) kept our Second floor key with him. After several request to him he denied to provide us the Key & also the loan papers & possession letter. Now situation is, We request him to sale out the Second Floor Flat & clear his all dues & rest payment return us, but not getting any positive response. We all forced him regarding to apply in Tata Delhi Power Limited & Delhi Jal Board for new connection but also he refused & tell us that he can arrange electricity & water to us from another house for a certain period of time & if we want from him then Rs.15000 we have to gave him. His one sister is a advocate & sitting in Tis Hazari Court, No one in the world says that the property is only two months old. Due to this issue my mother got a problem of BP low, ame with my Father & last few days back due to tension my Grand Mother got minor heart attack. I have two kids with me with wife. I request to all kindly suggest me what we do ?? as now we are totally helpless & also everyone in my family got depression due to that bloody builder..... Need help ....................