If he wants you to pay for passports so he can go abroad this year I’d decline. You’ve been more than reasonable offering to pay half.
The advantage if you paying is you can hold the passports. Incredibly significant imo. If he does buy them record the numbers and preferably take scans of the details pages. That way if you ever need to put a flag in them with passport control you can.
Tbh in your scenario waiting for him to take you to court would work in your favour as part of the cao you’d get a part that states that you can as resident parent take the children out of the country for max 28 consecutive days without his permission.
He however would still need your permission.
Asking where he’d be taking them isn’t unreasonable. Nor would be asking to see return tickets.
With regard the cost of the holiday you have no right to know how he’s paid for it. Technically he could have started work and still be at a point that the annual review for cms hasn’t happened so isn’t paying correctly – but legitimately so. He could have savings of a few thousands that he’d use. He could have someone paying for the break. The how though frustrating isn’t your concern.
If you believe that what the cms now hold has his income is now wrong contact them for a variation. As a separate issue.
