Legal Question in Real Estate Law in Texas

Yes, they still have a claim. You can sue them for their share of the taxes, and attempt to extinguish their claims. However, they still have an interest in the property until a judge says they don't. (Or unless they deed their shares to you.)

It is possible that the one who paid taxes acquired taxes acquired title under the doctrine of adverse possession. That heir should consult an attorney to see if he should go forward to obtain a declaratory judgment from a judge as to ownership.