Parties to the petition. - A petitioner shall join as respondents to his petition.

(a)Where the petitioner, in addition to claiming a declaration that the election of the returned candidate is void, claims a further declaration that he himself or any other candidate has been duly elected, all the contesting candidates other than the petitioner, and where no such further declaration is claimed, the returned candidates; and (b)any other candidate against whom allegations of any corrupt practice are made in the petition.