It is very hard to tell with what you have provided. Is there a court's order regarding custody? It appears that they both my be equally liable to pay the costs. Your friend should get an attorney and get back to court to enforce the divorce agreement along with reimbursement. A bigger issue is what is your friend doing to get the children insurance coverage? If he is paying child support, and pays for insurance he may be able to seek a deduction of his support as well.