Selling crypto to family members

Can I sell my BTC for fiat at market prices to friends (with split finances) or family members (shared finances)?

Asking from a tax standpoint (living in Australia, but interested in any infos independent of country that could help me find more infos).

As an example let’s say I bought 1 BTC for 10k AUD couple of years ago and sell it to my wife (shared bank account). Am I allowed to do this. Obviously I would pay CGT tax on it. Now let’s say I sell it to a friend (not shared finances). Am I allowed to do that? Lastly, the critical scenario. Let’s say bought 1 BTC at the ATH at 80k AUD and sell it to my wife now for 45k AUD. Can I claim a tax loss? Thanks for any infos on why this is not a thing are welcomed. I assume there is some law prohibiting this.