Hello. Thanks for contacting us.
I am so sorry to hear of this situation. It is wonderful that he has a sister who can take care of his affairs given the medical situation he is in. It is a true act of loving kindness.
I assume the court order governing child support is in NY, yes?
If so, yes, it is true in pure, wooden legal sense that child support continues as ordered unless there is a new order changing it. (A modification of child support order).
But the original child support order may state precisely at what point the support stops. If there was an administrative error and the payments continued despite the original order, then there is a strong case for return of assets. However, NY does not like to do this -- and the courts there have been reluctant to return overpayments. Usually, the amount is offset against future needs.
NY's narrow exceptions include a situation in which a father is forced to pay due to a judicial error in applying the child support statute.
In such a case, it will probably be necessary to get a lawyer to make this argument -- as unfair as it seems. The father's incapacity may also be a factor -- as courts are more sympathetic to a situation where someone was not monitoring his or her affairs when there is incapacity involved than where it is simply a matter of not paying attention.
Sadly, this is not something to be done with a form, because is it not a formulaic proceeding. You will need someone who is licensed by NY to practice law to assist (they don't have to live there, but need to be members of the NY Bar). I'd also recommend engaging a lawyer who regularly deals with similar issues.
If money makes this impossible, I can provide information about resources that can help people in need straighten out legal problems. However, I suspect it will require a trip to NY to make use of such services workable. If you need assistance with this information about legal help for those without resources to pay for it, please tell where the child support order was issued (what city in NY).
I wish you every success -- you are truly a wonderful sister to step in to get your brother's affairs in order when he can't do so himself.