[High fives] BrainWormsWontWin Brilliant work fellow Empath! 
OP - I'll just give you a little of my background because I realise I've just committed a monumental mistake in my life.
Went NC with D a few years ago but before I realised he was a N. Took weeks I had of silent phone calls, emails being hacked etc etc. Then, one day, it hit me how fucking atrocious my childhood was.
More time moved on. I made the assumption that mum was a fellow Empath. D becomes very ill. I break NC delibheratly in order to help M.
A few weeks ago, D confesses to MULTIPLE infidenlities through the years. I support M. But something about her reaction really bothered me. I tried to get her to live with me as a break for her but her reaction again just wasn't right.
A few nights on the phone she did something pretty bad - she attempted to prove me by saying a really hurtful comment. I was breaking my back supporting her. I ended the call and sat and reflected on all the other hurtful things, the neglect, the physical abuse that SHE had inflicted.
You see, the thought that I had not one, but two parents who were Ns was too much for my brain to cope with. So I ascribed a category for her (E) which was wholly undeserved. The are good reasons for that which I won't go into but don't I feel like a dick now.
Male Ns and female Ns whilst employing all the same manipulations and power plays do behave in different ways. Females are much more likely to take the softer softer approach and they too often fly under my radar.
But take your D. The use of contracts whilst utterly abusive is actually a really blunt tool. I wonder how intelligent he is?
Same goes for your M - how smart is she? Not all Ns are actually self-aware. They just know that acting a certain way yields certain results.
Oh and when you say moment of weakness? Sweetie, it's not weakness it is the energy and effort of keeping the NC in place. It's a tough place to be in.
Please message me if you need any more info.