So, basically, what happened was that he said he would agree to the change, conditional on suitable make-up time. If he doesn't agree to the make-up time being suitable, then he doesn't agree to the change, which means they revert to the orders.
He should e-mail her to clarify the events as they occurred in regard to the orders.
Dear Parent A,
You requested a change to the time the kids spend with me next weekend, I agreed conditional on appropriate make-up time being facilitated. Unfortunately, the make-up time you have offered is not appropriate, but I'd be happy to swap the weekends so that you have the kids from W to X, and I have the kids from Y to Z. If this doesn't work for you, that's not a problem, we will just follow the orders and retain the same weekend. I would also be happy to discuss an earlier pick-up time on Christmas Day if you'd like, perhaps 2:00pm? Please let me know. I also wish to advise that if the kids' time with me is not facilitated, I will be filing a contravention order application as soon as possible. Kind regards, Parent B.
If she still proceeds with withholding, then he file the contravention order application.