Harasment by mother in law and sister in law.

My daughter was married to my sister's son about 24 years ago. After one - two years marriage she started harassing and started demanding money. I kept her about money on some or other excuses hinting that she will send my daughter back home. In the mean time her daughter she left her husband and separated from her husband and joined her mother in harassing her. Both mother and daughter misguided her husband and started pressurizing my son in law to send my daughter back to my house. Ultimately he buckled and sent her to my house. After two years of separation he realized and left his mother and sister. His sister was interested in getting in her name all his property. She was successful in mission and all the property which was purchased by his earning of 12 years. She is still there and not joining her husband. My sister is holding whole of dowry and jewellery and given to her daughter. Please advise how can i obtain all the dower items, jewellery and money about Rs. 4,00,000 which i paid time to time.