Deed of Distribution and Lease offer

My mother and aunt are heirs to mineral rights (23N 59E) in Richland County MT. and the rights are recorded in Richland Co. There are already Leases written for the 50% of the mineral acreage, my mother and aunt own the other 50%. Recent conversations have brought up a ‘‘Deed of Distribution’’ how important is this form to have before they sign a Lease? Also, the already written Leases are for approx. 5 yrs and 20%. Is this the ‘‘going rate’’ or considered a fair offer/amount for Richland Co.? TIA