Bill, yes you (or someone) need to go through the records at the county courthouse. Then if you wish to confirm what you own (10 net acres, or some other amount) you'd follow the chain of title on the property from the initial USA patent up to the present. Once you have the legal description you can go to this site to find out who homesteaded it, www.GLOrecords.blm.gov .
After the homesteader patent you need to meticulously follow the deed from one owner to the next (making a copy of every deed for future reference). That will show you when, or if, a previous owner might have sold or segregated some of the mineral estate before you owned it. In other words, if Great Grandpa Joe left your Mom "1/10th" of his minerals you need to know if he still owned 100 acres of minerals, or 200 acres, at the time he deeded that "1/10th" to her.
To expedite your hunt start gathering all the information you can before you arrive in Crosby. Call the landman again to see if he can provide any more info. To get started some of what you want to know is;
A full legal description. The Township, Range, Section (or Sections), and the NW, SW, etc...
The party whom you ("our family") inherited from, ie... Great Grandpa Joe Buckalew, or Aunt Alice Jones...
The date (or at least year) these minerals were inherited from that party.
Why the landman believes it was inherited. Do they have a copies of a deed, a will, or some estate papers?
If their information was from a probate or estate, ask which county and state it was filed in.
Arrive early at the courthouse and explain to them you are new to this business. If they're not too busy they'll probably help you get going.
IF you have the full legal description, you can trace the ownership through the "Tract Books".
IF you have the party's name, you can trace prior and subsequent ownership of those minerals via the "Grantor & Grantee Index".
This is not rocket science, though it is a little too complex to fully describe here but either of the above avenues may get you going. Though be sure and gather all the information you can before leaving home. Depending upon the size of the property, and the number of hands this passed through, this could be a full day's effort. Just make copies of all the related deeds so you can review it more carefully after gathering your data. Good Luck