Prewetts + Remus
No, I didn't think so. Of your lot you're the only one with half a lick of sense. Not counting Lily. The answer to that question is unclear. Depends on how the Dark Mark works. And/or if another Death Eater knew enough to make their own using some artefact, or any number of other things. It's complicated. Still, if the oaths come into conflict and they're strong enough, it would be very bad.