Insurance companies could directly ask for DNA if they don't care about legality. And in return they could easily offer say 90% discount to 90% of the people.
You actually do not need to ask the insurred ones. You need a family member that is with another insurrance company and conclude from there?
All I am saying is insurance companies could ask and people will happily give their DNA for say 90% discount(which I think they could easily provide). They don't need family members or any other things or any other backdoor.