I am off to the UK on Thursday and have just noticed that my Australian passport only has 5 months left on it. I can travel out on my UK passport and come back in on the UK one with the Australian one there as proof of citizenship. Should I do the same with my son who is travelling with me or would he be best to use his Australian passport both ways. He's not feeling happy about being separated from me if we have to go through different passport controls, especially if I get taken to the side for checks.
You should enter the UK on the British passport and Australia on the Aussie one. Absolutely no need to show both anywhere.
No country on Earth requires their own passports to be valid beyond the arrival date, and many will even accept expired ones. Australia belongs to the former category.