Need advice on moving

Quick context, I (M28) live in a state as a co parent to 2 children under the age of 7.

Former partner has told me for the last year that she’s moving to another specific state (2 states away) and taking the kids regardless of if I stay or not. I’ve taken all the steps to have a job transfer and make everything as easy as possible just for her to tell me 28 days before the big move that she doesn’t want to leave anymore as she wants to stay in current state (she found a partner finally).

I’m in a very weird spot as there’s a couple issues:

If I stay she’ll move to another state, or if I move she’ll stay here.

I turned in my resignation letter months ago to the current company and someone’s already been hired for the position at the end of the month.

The transfer gives me ~$20,000 raise at the same job and would be union, and have better hours which means the kids would have more money every month alongside free health insurance.

What can I do