Dispute of flat between 2 daughters
My mother died 8 years ago leaving behind a flat in Mumbai. The flat was transferred to my sister and myself after she passed. Since then it has been on rent on and off. My sister wants to sell the property and I want to buy it, but she doesn't want to sell it to me and demanding for more money than market price. I tried offering the same amount that was offered buy a third party but she refused and wanted more if I wanted to buy. Now she is threatening to not allow me.to use the property or take 100% ownership. She stays in different state of India and has no intentions of owning the property. These things have escalated and now the conversations are painful and personal threatening to me and my family. She is threatening to put her children's name as owners in the property so that it becomes difficult for me to own the flat. I don't know what to do. She refused to pay any flat maintenance or other costs. She has paid the secretary of the building now together they have locked the flat so that I can't access.
I want to keep this flat until I am alive till as memory of my mother.
What should I do legally?