Royalties and general information

Ok, my mother died in 2004 and my grandfather left us mineral rights in doddridge wv. We signed leases in 2015. Well there are four heirs. They found oil and the proper papers were filed. Now the oil company is saying my step father is getting money. He never signed any papers . The oil company is saying now we have to file another affidavit with his name on it… at the clerks office. Is that even legal? And why should We? Can you give me some advice please. Over whelmed in california