Hi! I'll be glad to help you with this issue and follow up on Elliott's answer.
First, let me say that I agree with Elliott about her attempting to be manipulative. My sense is that she's being just plain nasty. I've seen this enough times with families I've worked with. That she has that "on authority from an attorney" is a code word for being unpleasant and mean spirited. Because, again, that I've worked with families means I've worked with attorneys who practice family law (divorce, custody, etc.). And no reputable attorney would want to set up such a situation. It's not only not enforceable, it's plain counterproductive. Here's why:
All you have to do is this:
You've already taken the wise precaution to keep communications in writing (good for you, I'm sincerely impressed). You merely have to add that "your husband [insert his name] asked me to communicate to you that we will pick up [name of stepson] at such and such a time". Now this has become direct communication from the boy's legal guardian.
Along with this, given that you're married to his father, you are in most states de facto a representative of the guardian husband. And no attorney would want to challenge this in court and look foolish.
But at this point, clearly she recognizes that you're on to her and she's desperately looking for ways to be a thorn and make things unpleasant. Your job, as the one with the upper hand (I bet you didn't see it like that before I said it) is to deflect her and keep on going. To not let her make her small jabs and her own unhappiness affect you more than minimally. Otherwise, she will keep on that same track.
Therefore, just adjust your email/text communications as I recommended above and keep on being the more sensible you and keep your good humor.
Okay, I wish you the very best!
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