VS I don't know how you can say you are comfortable in the UK on £30k/year. You must be living mortgage free.
£30k definitely not equivalent to $100k LOL.
Yes rental market for apartments isn't great at present.
If you have citizenship you are leaving the door open to return.
I hope the family will appreciate that you are moving back for them. The risk is that you move back and family just carry on with their lives..
Anything you can get for your business would be good and as others have said you don't want to give it away.
$400k unfortunatoey will not get you a lot in Brisbane these days. $500-600k on the other hand is a different matter!