He does not have to have an attorney for this matter.
What he needs to do is go to court on a modification of support order. Once he seeks getting a hearing for that he can provide the judge (which this will need to be filed in the county and with the court that originally order the support) with proof of him paying for other children, records from the dentist stating that the braces were optional (he has a right to these records as a parent), and that he is not responsible for an accident that the car insurance carrier is to pay for. He can submit his tax returns for the past 2 years, any and all bills for the children that are living with him, insurance statements if he pays that for her and the other children, mortgage payments, utilities, etc.
He can also argue that the support order was agreed upon prior to the law changing the age of emancipation and therefore should remain true to that law. (However, if the order is now changed in any way, they can argue that it is a new agreement by which the new law would affect.) Here is what the law state's in summary as provided HERE:
Under Indiana law, a parent's support obligation ends when the child turns age 21, unless the court finds it appropriate to order support for the child's education at institutions of higher learning (Ind. Code § 31-11-5-12(d)(1)). In deciding whether post-secondary educational support is appropriate, judges must consider (1) the child's aptitude and ability; (2) his reasonable ability to contribute to education expenses through work, loans, or other sources of financial aid reasonably available to him and each parent; (3) special medical, hospital, or dental expenses necessary to serve his best interests; (4) the ability of each parent to meet these expenses; and (5) fees mandated by federal child support program ("IV-D") rules (§ 31-16-6-2).
Judges issuing orders for post-secondary educational support must reduce other support orders for that child when they duplicate the education support order's coverage and would otherwise be paid to the custodial parent.
So, essential the decision is up to the judge. The best thing to do is NOT to get upset or defensive in front of the judge. Be respectful when the other party speaks, and keep your composure to stay on the good side of the judge. The more evidence he can have to prove that he should NOT have to pay, that he has paid as according to the terms of the original order, and that the child does not need continued support, the better outcome that will be had. To file for a modification hearing you can get the forms from the Clerk of Court or HERE if this case was originally heard in Indiana. For more information on representing yourself without an attorney go HERE.