5 night stop over in Shanghai - London to Melbourne 1 way. Would I need a transit visa & where from?

Myself and my 3 teens (they have a different surname) are flying from London (in Dec) to Melbourne. As we have never seen China - we wanted to stop in Shanghai for 5 nights en route. We are also Aussie passport holders, so are flying on the Aussie passport (dual UK holders). Would we require a transit or tourist visa? Do you have idea of the rough cost? Could we be entered as a family, or do we need separate visa's (all have our own passports). Can we apply on line - or do we have to go somewhere (we live 40miles from London). Any help would be very much appreciated :)