Honours information varies depending on the discipline. Information about honours in your chosen area will be available here shortly.
If you'd like to apply for joint honours, you need to negotiate this with the relevant honours coordinator for each department. You'll then need to complete a plan of study form, and have this signed by the two honours coordinators. This will also outline which seminars you will undertake and how your thesis will be supervised. You'll find a copy of the form in the Faculty of Arts and Social Sciences - Honours Provisions 2014 (pp 9-14).