hiding important information

Respected Sir, My older brother got married in april 2014. Just after 3 month of marriage my sister in law has started to behave like a mentally ill person. She stopped talking to my brother in their house and often gets angry and ends up using abusive words. My brother decided to seek psychiatric treatment for her health. Doctors have said “there must be some medical history in the past regarding her illness. The in-laws never told us regarding any of such illness before marriage. Moreover, now the girl has went back to her home. The in-laws are not treating our family well, threatening to kill us when we tried to converse with them. Currently from past 2 months the girl is staying with her parents and their is no dialogue between the 2 families. During this course our family has discovered some extremely shocking things: 1. The in-laws and girl told us that she has completed her B.sc degree before marriage. We have discovered that she had dropped out of her college and she never completed her degree. 2. We have discovered that the girl had already undergone a scissoring operation (conducted during delivering a baby, there are marks on her body) before her marriage. Our family is completely strangled as well as clueless as why these things were not revealed to us before marriage. We suspect that the girl must have married earlier or done something which is socially unacceptable. These things were not told to us even though we had inquired the same before marriage. Currently the in laws are neither willing to engage in a dialogue nor the are sending the girl back to my brother. What shouid our family do? We don’t want to continue this relation anymore.