That shouldn't be a problem, though having British passports makes things a lot simpler. When they query at the border, which they will, just show their and your birth certificates and your marriage certificate, and as they are British, you are getting their passport in UK. I assume you are British otherwise than by descent, e.g. born in UK?
I suggest he doesn't volunteer this information at first. Write on the immigration card his expected length of stay as 3 months. If they ask what he is going to do and where he is going to stay, he can then say he will be staying with you. If they then start asking questions about ties in Australia, his job etc, then disclose his plans about applying for spouse visa in Australia once you meet the financial requirement.