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Agreed ... if you are claiming the kids on your return then you must have the information on the 1095-A and you and the ex must agree on how the PTC is allocated between your and their tax returns.  Between both of you it must be 100%  but you can allocate it any way you  both can agree to.   If they have already filed and took 100% then you will only take 0% unless you wish to have a fight on your hands.   Of course, if you can agree to work together, then you both could win.