Former Aurors.
I agree with most of those I know of, and trust your judgement on others. I've also been vaguely keeping tabs on Aida Shafiq as a "think outside the box" experiment. She just tends to be very vocal against any criticism of the Ministry, but it could just be a kissing up thing. Time will tell.
Greyback is definitely a Death Eater. Or, actually, I have no idea if he's officially in the club, but he's very closely allied with them in any case. Might still technically be doing his ~*~own thing~*~, though.