(a) Except as provided in § 725.361, no person other than the Secretary of Labor and authorized personnel of the Department of Labor shall participate at any stage in the adjudication of a claim for benefits under this part, unless such person is determined by the appropriate adjudication officer to qualify under the provisions of this section as a party to the claim. The following persons shall be parties:
(1) The claimant;
(2) A person other than a claimant, authorized to execute a claim on such claimant's behalf under § 725.301;
(3) Any coal mine operator notified under § 725.407 of its possible liability for the claim;
(4) Any insurance carrier of such operator; and
(5) The Director in all proceedings relating to a claim for benefits under this part.
(b) A widow, child, parent, brother, or sister, or the representative of a decedent's estate, who makes a showing in writing that his or her rights with respect to benefits may be prejudiced by a decision of an adjudication officer, may be made a party.
(c) Any coal mine operator or prior operator or insurance carrier which has not been notified under § 725.407 and which makes a showing in writing that its rights may be prejudiced by a decision of an adjudication officer may be made a party.
(d) Any other individual may be made a party if that individual's rights with respect to benefits may be prejudiced by a decision to be made.