Your detailed explanation leaves me a bit confused, however, I will try to provide some insight into Problem 3 (your last item.) Others here on Moodle.org might offer more ideas.
If it was me, I would delete the quiz attempts and email the students saying "You need to retake Quiz #5. Sorry."
If it was me, I would delete the quiz attempts and email the students saying "You need to retake Quiz #5. Sorry."