OK, more seriously, there's something wrong with your test if you think you're getting negative resistance. With coils, even accurate resistance measurements may not tell the story.

Have you tried swapping two coils? Swapping two plugs? What makes you suspect #3 other than those measurements?

And for those Physics fans, negative resistance is not possible according to our present understanding of Physics. Last guy I met that even got zero resistance had a Nobel prize for the effort. Negative resistance would be an even bigger deal. But BTW, "they" probably thought zero was impossible too, before they found it was not.

__________________
2001 X5 3.0i, 203k miles, AT, owned since 2014