Newbie question about mineral rights in California (Central Valley Area)


I just registered, new to this site and just navigating through the forum. I have a few questions and I hope someone can point me in the right direction. I hope I am posting in the correct area and I want to give a little history. I recently became power of attorney for my grandmother and coincidentially was contacted by a landman regarding mineral rights leasing. I met with the landman a week ago and listened to his proposal and he gave me a blank lease to review. He stated that his company has been contracted to secure 50,000 to 100,000 acres in the area for an operator and is interested in 80 acres of hers. There was some exploration done in the area about 25 years ago and nothing else that I am aware of. A well was actually drilled with no real results and this location is about three miles from her property. I googled his company, searched the web for additional information on mineral lease's and I a a little overwhelmed. Since, this is all new to me, I want to make sure that the lease is actually a good deal and that I am not dealing with a flipper. We have had some additional conversations over the telephone and he called me yesterday and stated he was back in area and had a lease for me to review and sign. He also stated that he had been given approval for an additional 450 acres of hers, but it would be on a seperate lease and forthcoming. All of her property is continous. I took the lease and stated I wanted to have an attorney review and that I would be in contact. The lease is actually written with the name of the the broker is for 5 years but does reference 20 years..and now for a few questions..

Is it normal for the oil and gas lease to be made with the broker and not the operator.

The lease has no signing bonus, but they are willing to lease her 50% interest at $15/acre and 1/6 royalties. Is there a way to find out if this is a reasonable offer.

What areas of lease should I be looking at to question further or understand more clearly. In other words, are there any generic terms and/or clauses that I should be looking for.

Any help or advice is welcomed.