Assuming your great-great-grandfather owned the minerals at the time of his death, the current owners now of what he owned THEN would be determined by looking at who his heirs were, then figuring out who his heirs' heirs were, etc. This is done by probate documents, when present, and by applying the laws of descent and distribution in West Virginia, about which I know nothing. Based upon those two things, your cousin might or might not be entitled to anything. Since you and your sister are receiving royalty checks, that means your minerals are in production. When that is the case, it rarely makes sense to sell the minerals. Usually, the royalty stream of income will exceed whatever price per acre you are offered to sell your minerals.