Sale of oil & gas rights

We have about 24 net mineral acres as part of a total family acreage of about 120. Parcels 3.7.19 and 3.7.19-1 in Cameron district, Marshall County. Coal was sold off long ago, currently have oil/ gas in play.

There has been some recent contact offering to buy outright and as we are all getting up in years, likely will sell rather than pursue a lease.

What is going rate range for outright sale? Hiw about lease? What should we know before signing a sales agreement and is it worth getting an attorney or advisor for 24 acres?

TIA~