Upon the filing of a petition for specific execution of the contract, the court shall fix the time and place for hearing thereon. Notice of the filing of the petition and of the time and place of hearing thereon, together with a copy of the petition, shall be served on the executor or administrator twenty days before the date of the hearing. The court may order notice of the filing of the petition and of the time and place of hearing to be served by registered mail on the interested heirs or devisees whose addresses appear in the court’s file and records in the estate. Any interested heir or devisee may appear and intervene, upon written application to intervene filed prior to the time of the hearing.