I am having the same problem with parents being attached to other people. When I use the relationship button, it will not let me edit.
I could not detach the parents from the wrong person. My example, Tom McAdory was correct as the father of James McAdory. He also showed up as the father of John Reynolds. I finally deleted Tom altogether. When I added him back as the father of James, he also showed up again, immediately as the father of John Reynolds.
Very frustrating. What can I do?