1rudeboy is confused as usual. zero exemptions will maximize your tax withholdings, not your take-home. The more exemptions you claim the less tax withheld and the higher your take home.
You can download a W4 form and use the worksheet to help calculate how many exemptions you should claim.
However, the advice posted earlier about the ex is valid. In the absence of a legal agreement on how to split the tax credits, the person who gets to claim them is who the kids live with more than 50% of the time. And that needs to be documented.
That comment screams, "internet butthurt."
She lives in a different county (different school taxes) and my kids are picked up daily at my own home (i.e., it's on the School districts roster where they are at time of pickup). Not much more evidence is need than that.