Whatever your dispute with your wife is, that is separate to the authority of the agent.
As an owner, you can instruct the agent that the property is not to be let and the agent must cease activity accordingly unless and until (a) they receive clear instructions from all owners or (b) there's a court order.
As against the tenant, without valid notice and the required time frame (2 months in these circumstances), they cannot be compelled to leave without a court order.
When I say 'court order' I also include an order you might get from QCAT (as it is a court of record, despite being a tribunal).
As an owner, you can instruct the agent that the property is not to be let and the agent must cease activity accordingly unless and until (a) they receive clear instructions from all owners or (b) there's a court order.
As against the tenant, without valid notice and the required time frame (2 months in these circumstances), they cannot be compelled to leave without a court order.
When I say 'court order' I also include an order you might get from QCAT (as it is a court of record, despite being a tribunal).