Universal health coverage is the only way to eliminate unfairness. My father had Huntington disease, but I've had a test showing that I don't have the gene. Several of my family members have had testing for breast cancer-associated genetic mutations. Otherwise, all you have to tell the company, if asked, is whether they've actually had cancer. Usually questions about family don't extend to distant relatives.
Research is different from clinical care.
Research records are NOT part of your medical record. Insurance companies are not usually permitted access to research records. I was tested as part of a research project. Its legality is questionable. If insurers know the shadow chart exists, they can get at it.