Legal Question in Wills and Trusts in Illinois

Yes, if she properly and timely files a claim against your father's estate, and proves it.

You should seek legal representation. If he was not entitled to anything from the estate, then arguably your giving him a share was a gift and the child support remains a matter between your brother and his ex. He was not legally entitled to anything from the estate or from you. That said, you are suggesting (and posting) that you received the estate, arguably, to hold and distribute in keeping with your father's wishes. Theoretically, that may open up some arguments. In my view, the ex would be best advised to pursue your brother directly.

In that regard, perhaps you should approach your brother to suggest that it may be a good time to work with an attorney to resolve his defaults in providing for his child(ren). It is not clear what he has received, but perhaps legal fees can be saved and the children more promptly receive what is allocated for their benefit than if continued collection is forced in lieu of acting responsibly.