Trailing spouse postdoc
There's no point in disguising the reason for you moving to Australia. If you give some kind of prevaricating answer to the question of why you're moving, then this will look unprofessional at best. The people with whom you're going to chat about possible postdoc positions for yourself will of course know about the academic two-body problem. 

The fact that there are two institutions where you might be able to find work is in your favour. Cultivate your contacts and opportunities with both institutions, at the same time. Don't be coy about the fact you're shopping around for positions.