Inherited mineral rights

Recently we found my father, who was killed in WWII, had inherited 2/9 interest in mineral rights and property from his grandfather Marion T Pierce of Carter Co. Oklahoma. After he was killed all contact with Pierce family was lost. The other family members still have these mineral rights and property. We have gone through probate but how do we establish our 2/9th interest again.

Did you father have a probate done in Oklahoma?

If so, unless there was a tax deed or quiet title suit that took your father's ownership away, you've established it. You should check to see if there is production in the section, and you should make sure you have a document on file with your current address on it. If both of those are done, you've done what needs to be done. Its possible there is no production, no there is nothing to claim (for now).

Yes we had it done in Carter Co. Oklahoma. There are producing wells. Oklahoma Treasurer is holding some of the money. How do we notify the oil companies that are pumping.

If you know who the operator is, then send them a letter with a copy of the final decree or distribution of estate (the final order that determines who inherited from your father), and that should be all.

Now, if I'm missing a part of the question, then let me know.