Robert,
If you sign the "Affidavits of Death and Heirship" purporting that you and your sister are the only heirs-at-law of your grandfather's mineral interest and then it turns out that you are not because you followed some of the irresponsible, unprofessional, ridiculous advice on this Forum and failed to locate a Probate that affected the chain of title, then you will have filed something in the public record that is FALSE.
In probably every state in this country, that is a criminal offense if it was done under certain circumstances. In my state, I believe that means that one knew or should have known that the facts sworn to were not true, regardless of whether or not one's intent was to defraud. I have no idea what the circumstances would be in Oklahoma. Would you be prosecuted for filing what later turned out to be a false AOH? Not likely, and I never said that doing so would automatically result in investigation, arrest, or prosecution in your specific case or any other case. I admit that there is a tiny chance that would happen, but nevertheless it could happen, based upon how Oklahoma's Penal Code is worded and based upon what side of the bed the local prosecutor woke up on that day. So why on Earth would you even want to take that chance? I reported somebody who had filed a false AOH to my local prosecutor, and he definitely was interested. So it does happen!
If you are willing to swear out and file AOHs claiming that you and your sister are the only heirs-at-law of that mineral interest, then yes, the company is likely to "recognize" your rights and start paying you. But again, what if something you filed in the public record turned out to be FALSE? Then you will have created a "cloud" on your title and potentially taken money that does not belong to you, not problems that I am guessing you either want or need.
So if you want to do the quickest, easiest, least expensive thing that will get you some money as fast as possible, and you don't care about any potential consequences, then by all means stop reading this, go sign the "Affidavits of Death and Heirship" right away, return them, and get on with your life! Otherwise, if you are a prudent, responsible individual to whom the thought of filing a potentially FALSE AOH is anathema, even if done so with good intentions and even if there is zero chance that you would be prosecuted, then consider the following steps BEFORE filing any AOHs in the public record:
(1) Check for a Last Will and Testament that was filed in a Probate Court for the Estates of your grandfather, grandmother, mother, or father. To do this, somebody would have to check with the Probate Clerk in as many as three places for each of the four Decedents: the County where the Decedent last lived, the County where the Decedent died, and the County where the Decedent owned any property. In most cases, all three of those places will be the same for each of the four Decedents. But do your best to search in other Counties if necessary to increase your comfort level of ascertaining the truth.
(2) For as many of the four names for which you do find a Probate that was not in Pittsburgh County, Oklahoma, obtain a certified copy of that Probate and file it in the Deed Records of Pittsburgh County, Oklahoma, if one was not already filed there back in the day.
(3) So now, for each of the four persons you should have either (a) a Probate filed in Pittsburgh County, Oklahoma, or (b) a Certified Copy of Probate filed in Pittsburgh County, Oklahoma, or (c) neither a Probate nor a Certified Copy of Probate filed in any of the three places you looked.
(4) For as many of the four names that fall into Category (a) or (b) above, obtain a photocopy of it and send it to the company that has your money. There is no need to complete an AOH for any of the four names that fall into Category (a) or (b) above.
(5) For as many of the four names that fall into Category (c) above, go ahead and complete the AOH, file it in the Deed Records of Pittsburgh County, Oklahoma, obtain a photocopy of the filed AOH, and send it to the company that has your money.
If you complete all of these steps, you should have created a solid chain of title between your grandfather and you and your sister, you will have "proven up" your ownership to the company so that they will no longer have any reason to withhold your royalties, and you will have minimized any future title issues that might have arisen from this heirship.
Good luck to you,
P. W.