|(a) Intervention. A person who may be affected by a decision of TRS in the proceeding may file a written motion to intervene at least 15 days in advance of the hearing date. The person may request an opportunity to present any relevant, material, and proper testimony and evidence bearing upon the request to intervene. (b) Joinder of parties. A party may move to join other persons as parties to the proceeding if they may be affected by a final decision of TRS. A motion to join other parties shall identify the person by name, address, and telephone number; shall state the nature of the other person's relationship to the proceeding or potential interest in the proceeding; and shall state why the person is needed for the just adjudication of the appeal or other grounds for the motion. The motion shall also state whether joinder of the person is feasible. If the motion is granted, the person shall be a party to the proceeding.