Sam,
I've done dozens of mining deals over the last 35+ years. Many are in Nevada where I personally control several hundred claims. Mining leases are extremely complicated and much longer term than oil and gas leases. Mining projects often require more than twenty times the capital expenditures of the most expensive horizontal oil wells before the mining company sees the first unit of production that is salable. Consequently the risk analyses are totally different between mining and oil.
That said, 2.5% royalty on gross sales of refined product for an open pit sand operation is on the low side for leases negotiated today but not by much. Greedy lessors demanding 5% usually give up their land for 20 years and get 5% of nothing while lessors who understand mining risk and lease structure and who use experienced mining law firms to negotiate leases will generate consistent cash over the term of a lease.
To make sure you are getting a fair deal under the existing lease, you should set aside $5,000 from he next royalty check and have an experienced mining lawyer, audit your leasehold rights. Most mining lawyers are associated with mining engineers and together they can give you a report tha will help you understand your options and fair market value of the existing lease.
In Nevada, mining permits are very highly regulated and under modification; sometimes as often as annually. As a lessor, your family should know in advance when your claims are to be included in future mining operations. That knowledge, with monitoring, will allow the family to have confidence that it isn't getting screwed. Most Nevada experienced engineers and lawyers work closely with regulators especially when the "claims" are on federal lands. (You didn't mention if your claims were patented or unpatented and it makes a huge difference in a mining lease.)
Contact me via PM on MRF if you need names. I've had the privilege of working with the best.
Gary L Hutchinson