Hi

Consumer Credit laws say that if you have to sell your house to be able to afford a loan (or 4?) then you could not afford it in the first place…. see
The contract will be unsuitable for the consumer if, at the time the licensee provides the credit assistance, it is likely that:
(a) the consumer will be unable to comply with the consumer’s financial obligations under the contract, or could only comply with substantial hardship; or
(b) the contract will not meet the consumer’s requirements or objectives; or
(c) if the regulations prescribe circumstances in which a credit contract is unsuitable—those circumstances will apply to the contract;
if the contract is entered in the period proposed for it to be entered or the credit limit is increased in the period proposed for it to be increased.
(3) For the purposes of paragraph (2)(a), it is presumed that, if the consumer could only comply with the consumer’s financial obligations under the contract by selling the consumer’s principal place of residence, the consumer could only comply with those obligations with substantial hardship, unless the contrary is proved.

I would be asking the ‘broker’ and subsequent lenders to provide a copy of your credit file and all documentation that addressed the ‘suitability’ of the credit contracts.
You still have contractual issues but these can be resolved with time – which can be bought from the Financial Ombudsman.

I would be highly surprised if Company X finance would stand up to scrutiny.

My message …. perhaps there is light – be very discerning about ‘traditional’ legal advice.

Look to the finance contracts and use the credit act. We all make stupid (and good) decisions – the Crdeit Act says that you must ahve been able to AFFORD it.

see https://fos.org.au/ and ASIC – read the legislation and codes of conduct, VERIFY your credit contracts line by line.
Your father got himself into this … rest assured he can prevail – do the work and you/he will get through it.