This might be an unpopular opinion, but maybe you need to err on the side of being firm but really softening the message. Your W may be completely wrong about you and vilifying you, but as they say, her perception is her reality. I know that I get triggered when I get a plain “no” response. Would it work it cushion it a bit so that there is no way any sane person could say you were being anything but amicable? For example “Sorry, no that won’t work for me.” ?
To be clear, I mean this for your sake, your sanity in communicating with her/co-parenting and your protection in the event of D proceedings.
Thank you for the feedback, I think it makes sense.
For the example I mentioned, I did say more than No. I think I said something to the effect of, "No that doesn't work for me, I already gave you one of my nights to you and I would like time with the kids." When pressed she will put me on the defensive.
Your point about softening my messaging is well-taken, though. I will explore ways to do this.
One thing I have tried is the positive lead-in, or pos-neg-pos sandwich. For instance, I may text her:
"Hope you are having a good time with the kids. I wanted to remind you we need to discuss XYZ so we can firm up our schedule."
The little positivity seems to help. It goes against strict DB advice, but I consider it acceptable because I am not looking for a reconciliatory reaction out of her.