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If the property is in Texas, one place to start, at least online, would be with the online county records where the land is located.

Most Texas counties are online now and some (not all) have a filter by which not only surface owners can be searched but also mineral owners.

Property taxes owed will also be shown. At least they have been on the particular counties I've searched.

Start with the 'named' County Appraisal District then look for property owners and go from there. Google is your friend here. For example, search "Gonzales County Appraisal District", (or any county) and good luck with your situation.

You may be able to go in with more information than your greedy sibling.