Regarding your last two questions, on how to know if leases in mother in laws files have expired, and whether there might be more than one leasing company (lessee) per tract…If royalties are currently being on a tract that indicates there is an active lease, but you will need to determine if all your acreage was included in the producing unit or portions of the acreage were excluded and the lease on that part possibly expired. That could depend on whether the lease included wording like a Pugh clause or depth clauses.
On the tracts where no royalties are being paid, look at the lease term of the most recent lease in each of those files. If, for example, a non-producing lease says it was for a primary term of 5 years beginning on January 1, 2014 then that lease may have expired this month. If leases included extension options you’ll need to determine if the options were exercised extending the original lease term.
On any of those most recent leases where the lease term indicates they have expired, mail a registered letter to the lessee named in the lease and request that they record a release in the deed records to document that their lease terminated. Depending how long ago the primary term of a lease expired you may find the leasing company has gone out of business, or an original lessee assigned the lease to another company. Some operators may resist providing you a release if the wording in your lease doesn’t specifically require it, but is logical to ask for and should at the least allow you to determine if the lessee thinks they still have a valid lease.