It sounds like you are a pretty private person. I told the small number of people closest to me when my family member became ill. I don’t think there is a lack of dignity in being ill, so that did not occur to me. I do not disclose diagnosis because that is my family member’s information to share. Two of my close people responded in consistent and helpful ways, which doubled the core team. AND the rest of the family is very supportive in their own ways.
I’ve drifted away from friends throughout this process and lots of people have talked about us. Mental illness is medical illness. I feel the same as if my family member were diagnosed with any serious illness, though the challenges are much different. You are right, people do respond differently to mental illness than to somatic illness. That’s not a problem I can solve so I act as if the progress against stigma has been made. Then I just cry or get angry when we face stigma, but that’s not too frequently.
NAMI has a class called Family to Family for general education about mental illness and many chapters have support groups for family and friends of people with mental illness. There might be people nearby to meet with and we are here on the internet to support you.
I hope the best for your family. Does your son go to counseling or accept medical treatment? If so, some depression, anxiety, and psychosis can become less burdensome for him. People can recover quite a bit.