Q: So if my ex and I have an agreement ( verbal, through text, as we are not communicating that well right now)

A: For the agreement, until a document is signed/notarized and approved by a court, any agreement is not locked. The text is evidence of an agreement (and can be admitted to evidence as a prior agreement/performance), but private agreements can always be modified in a court filing (there are some limited exceptions if both parties agree to not litigate previously agreed matters). The situation where private agreements are generally not re-reviewed by a court is if both parties agreed to private mediation. Even then, from a technical perspective a private agreement is not enforceable by a court until the court has reviewed (and approved) the agreement.

For the taxes, I'm not sure exactly what was said, but the concept that you would have to pay your ex (not the IRS) for back taxes seems very suspicious. For tax purposes, until you are formally divorced (with a final decree), you are still married. As a result, both spouses are jointly and separately liable for the other's acts. There are exceptions to this liability rule. First, some circumstances allow an "innocent spouse" exception. Second, if you filed as "married filing separately" you cannot be held liable for the acts of the other spouse.

Since this matter revolves around claiming dependents, the matter is quite simple. Here is a link to the 4-part test: http://www.intotolegal.com/upcoming%20Events/Qualifying%20Child.html . Whichever parent meets the requirement for each individual child can legally claim the child as a dependent. If both parents try to claim the children, an audit will occur. If this happens, both parties must appear and the IRS decided which parent gets to claim the child(ren) based on the 4-part test.

A: If he put into writing that you could claim all three kids for 2016 and you did, and has now filed a motion, I think you will prevail on that motion. Make sure you file a response within 21 days of his motion and I would consider attaching the text chain. If I knew more specifics I might be able to provide further insight. If, for example, he owes you child support for 2016 that has not been paid, he may technically have lost his right to claim the kids anyway. You might consider consulting with an attorney to deal with this.