No. Section 265 (2) (b) of the Australian Road Rules states that a person must not occupy the same seating position as another passenger (See 1 in Appendix).
265—Wearing of seatbelts by passengers 16 years old or older
(1)A passenger in or on a motor vehicle that is moving, or that is stationary but not parked, must comply with subrule
(2) if he or she—
(a)is 16 years old or older; and
(b)is not exempt from wearing a seatbelt under rule 267.
(a)must occupy a seating position that is fitted with an approved seatbelt; and
(b)must not occupy the same seating position as another passenger (whether or not the other passenger is exempt from wearing a seatbelt under rule 267); and
(c)must wear the seatbelt properly adjusted and fastened. Note 1— Approved seatbelt is defined in the dictionary
Note 2— Subrule (4) provides that subrule (2)(b) does not apply to passengers holding children under 1 year old in their laps on buses, minibuses, taxis and tow trucks in certain circumstances. Bus and taxi are defined in the dictionary.