Hey JJin -
I agree with Mr. Mallory - you will need to learn more about the state laws in whatever state the property is located in. And you should definitely consult an attorney on anything like this.
And I agree with Mr. Hutchison in that the amount of land and potential income would certainly be effective issues in justifying the potential expenses involved. But would like to add that the location of the subject land(s) is also very important.
You will need to determine each of the parties' last place of residence and whether any of them left a Will that was probated (or if any Administration was had on their estates). If so, you will need certified copies of those matters to file in whatever county the subject interests are located in.
In most states, Probate law for Intestate Succession (no Will) allows for the interests to first go back to the deceased person's parents. If they pre-deceased the decedent, then the interest goes to their siblings and their siblings' heirs, per stirpes (each gets their fair share). If they had no siblings, then there is a system for the interest to go to cousins, but I'd have to look that sort of thing up.
Minimum, you will need an Affidavit of Marital and Family History or an Affidavit of Heirship on the entire family or on each of the separate families to establish who you are in relation to the various deceased parties.
I hope you like genealogy, because if you have to hire someone to do it, this sort of thing can get expensive. It could take months to gather up all of the necessary information and prepare whatever documents you need to clear title into you. I know, because I do it for a living. I prepared a family tree on my Grandmother's family one time (she was one of nine children) and it took me 3-1/2 years to gather all the information and prepare all the documents. The final report (we didn't need affidavits) was over 100 pages long.
The least expensive way to do what you want to do is to wait until a Landman comes along wanting to lease your interests. Supply him with what information you have on your distant, now deceased, relatives and he or she will gather up the certified copies and prepare the Affidavit(s) for you for FREE, 90-Days Same As Cash.
And request duplicate originals of any affidavits they prepare - sometimes those just get stuck in an oil company's files and never filed in the county records. If you have a duplicate original, you can file it/them youself.
Hope this helps -
Charles
Charles Emery Tooke III
Certified Professional Landman
Fort Worth, Texas