Rita Kerai

I am looking to do the Aged Parent Visa (onshore) for my folks once the borders open up in Perth. They are UK citizens but have been residing in India for past 6 years. Their house in London is on rent. I have heard that if they fly direct from India to Perth, they wont qualify for medicare as passport stamp will show they have been in India for quite some time. My questions are: 1. If they fly from India to Perth, do they still qualify for the UK recipricol health benefit here for medicare? Is this true? 2. Do they have to fly from the UK to show they are residing there? if so, how long would they need to be in the UK for before coming to Perth? 3. What proof of documents would need to be shown to confirm residing in UK? They have no utility bills etc under their name as current house in on rent. When they go back to the UK, they stay with my sister. Any help/guidance is appreciated. Thanks in advance