The court must, on a party’s request, or may, on its own initiative, order witnesses excluded so that they cannot hear the testimony of other witnesses. This rule does not authorize the exclusion of:
(a) a party who is a natural person or the spouse of such natural person;
(b) an officer or employee designated as a representative of a party who is not a natural person; or
(c) a person whose presence is shown by a party to be essential to the presentation of the party’s case.