I hope LW finds a therapist to talk this through with. Someone they can lay it all out to and get help to figure out what to do. And then the therapist can help them deal with the fallout.

I think LW is going to have to tell the sister. I see a test that more directly compares the sister and the adoptee in the future. Or LW showing up to a family event and being introduced to a "new sibling".

Those ancestry DNA sites are gross for several reasons. Digging up ghosts is one of them.