Since it is your wife's grandfather's property, it devolves equally on both his sons upon his intestate death. Now both the sons have died hence their legal heirs are entitled to their fathers' respective shares.
In fact your father in law had two children out of which one died, it is not known whether he was married and survived by his wife and children upon his death, if so, your father in law's share in the property shall again be shared between your wife and her brother's family members.
This is the position of law. For further clarification you may produce the relevant documents before a local lawyer and can proceed as per his advice.