Upon application to the arbitration panel by a party, a person who is subject to service of process over the subject matter of the arbitration shall be joined as a party in the action if (1) in his absence complete relief cannot be accorded among those already parties, (2) he claims an interest relating to the subject of the action and is so situate that the disposition of the action in his absence may (i) as a practical matter impair or impede his ability to protect that interest or (ii) lead any of the persons already parties subject to a substantial risk of incurred double, multiple, or otherwise inconsistent obligations by reason of his claimed interest. If he has not been so joined, the arbitrators shall order that he be made a party. Any person joined as a party to the arbitration shall have the same time to answer which was given to the initial defendant in the case.