Step son has no legal right to inherit from step mother
Had your mother predeceased your father then the father's children would have inheritance rights. However, since that is not the case, I agree with all of the other responders - without a will stating otherwise, the law of Intestate...
The executor has a duty to fulfill the terms of a will
Since your brother, as executor, is not complying with the duties and terms set forth in your father's will, you need to petition the court that has jurisdiction over the Will (probate court in your county) and request your brother be...