Your in-laws have lost their daughter and they must not be in the right state to think properly. Every parent has a special bond with their children, similarly, your in-laws must have a special bond with your wife. It’s hard for them to believe that their daughter is no more with them. Many theories must be going on in their minds. Although they know that your wife died due to health problems but they might not be ready to accept that. Being in that mental state, they want to blame their daughter’s death on someone. Some parents blame themselves and others blame the doctor but in your case, your in-laws are blaming you. So, you need to handle this matter very carefully. We would suggest you to pursue convincing your in-laws that you are not the person to be blamed. And hire a good lawyer to prove your innocence in court.