Offers to buy usually come because the buyer knows something. I see a permit for a horizontal well in sec 14 heading north into section 1. Not sure if they are swinging the well through 12m but given the name of the well, it looks like it. HA RA SU65:RIIS OR 14-13-12-1HU 1-ALT. It was spud in October, So if it were me, I wouldn’t sell with an active well in or nearby. I would want the royalties. You have room in 12 for several more infill wells.
It is normal for royalties to decline over time. The wells are producing a finite resource and the pressure and volumes decrease over the lifetime of the wells. Prices also change all of the time.