And I’m still angry about it after several years.
I'm part of various trials and they make it very clear that nobody will get any personal feedback. The data is anonymised. If the trials didn't state this in the contract, they should have. They are usually very careful. But often people don't read the paperwork.e
I am part of the Decode ME trial. I think a lot of people signed up because they thought they would get personal answers, but they should have checked the small print. We do these large trials to take forward science, not for our own ends.
But to answer B's question. Yes, you all need to know, because diseases like Parkinsons and some dementias start decades before you have noticable symptoms and there is very much more to you can do to address them in your 40s and 50s than if you leave it too late. Head in the sand is no good to anyone.
Get scanned. Self check. Do genetic testing. Take prophylactic actions. Take advanatage of all the scientific advances you can. Learn whatever you can so that you can tell your family of any predispositions they might have. My father's family were very secretive about their diagnoses, even though it have might help extended family to know (in some cases). The selfishness still makes me furious.