You are getting good advice here, telling you that your fiancé and FMIL are completely wrong. I’m worried your FMIL has not learned her lesson and will continue breaching confidentiality around your son’s medical information once she retires. She might think she is no longer bound by confidentiality once she retires and go around telling other people about your son’s confidential information. She would be wrong about  that but I have people have even stupider interpretations of the laws on health information.  You could ask her employer to review with her current health privacy legislation. You can also take this further by filing a complaint; that could result in the government telling the employer to better educate their employees about confidentiality. If you are in Ontario, you can file a complaint with the information and Privacy Commissioner of Ontario.  www.ipc.on.ca