There are a number of different factors that affect value. For example, whether or not the lease is held by production, and if so, whether the production is holding all depths, what the lease royalty is, who the operator is, location, whether the minerals are burdened by non-participating royalty interests, whether there is a drilling permit on the property...the list goes on.
24 net acres is a sizable position, and with lease/purchase values having skyrocketed in the past year, it is worth a lot. Often, when you see a large uptick in purchase offers all of a sudden, it corresponds with lease expiration dates nearing, an assignment of the leases to an active operator, or a drilling permit issued. While others may disagree, it is near impossible to sell minerals in this area for a price that is equivalent to what your royalties would be if a few wells are drilled. You could try reaching out to the forum sponsors for information on what prices they're seeing in that area, but odds are the offers will only go up as time goes on. Best of luck to your relative!