"Mad House: Growing Up in the Shadow of Mentally Ill Siblings" by Clea Simon
If you are a sibling of someone with mental illness, I recommend the book "Mad House: Growing Up in the Shadow of Mentally Ill Siblings" by Clea Simon.
Most support resources like NAMI are mainly for the primary caregivers, who are usually parents, or else for the people with mental illness themselves, as these two groups have the most need. The same goes for all the famous books and memoirs.
Due to the family dynamics around severe mental illness, the perspective of siblings is usually ignored and silenced. Everybody has bigger things to worry about, and the job of the healthy sibling is to be healthy and happy, for them to experience problems of their own is experienced by the overwhelmed parents as dereliction of duty.
Clea Simon's book is written from a unique perspective. Considered on its own, this perspective may seem very self-centered, ignoring the bigger challenges of others. In the larger context of all the conversations around mental illness, this self-centered perspective is useful, as most discussion ignores siblings entirely.
It is almost 30 years old and only available on paper, no ebook. But can be bought on Amazon.
If you are a parent, not a sibling, I do not recommend reading the book, as it will probably make you feel bad and resentful, and also will not help you with the hard challenges you face. The same if you have a diagnosis yourself.