No person may hold more than one membership, and no fractional memberships may be held, provided, however, that:
(a) Two or more persons may have an indivisible interest in a single membership when authorized by, and in such manner or under the circumstances prescribed by, the articles or bylaws; and
(b) If the articles or bylaws provide for classes of membership in which the differences are not merely the number of votes entitled to be cast by members of the class, and if the articles or bylaws permit a person to be a member of more than one class, a person may hold a membership in one or more classes.