I wholeheartedly agree with your points but this bolded bit - this is where the crux of the issue is IMO and it can probably be worked out from his MO and 'the likelihood of...' because god knows we're unlikely to get the truth from him or anyone protecting him.
His family and acquaintances probably don't perceive that they are protecting an abuser and serious criminal but they sure are - protecting, covering, enabling, facilitating is a choice to promote evil. I hope they can come to see this. Maybe RB has been mixed up with some far scarier criminals and they daren't tell anything due to possible repercussions?
Anyhow, your bit in bold, I agree that it would be far far too risky for RB to have Marion with him in Aus and it doesn't really make any sense why he would - she'd be a loose cannon, most especially if she were to contact any family member, and he'd long since perfected the art of fraud without needing her presence. He may well have needed a female accomplice. If Marion did come back on the different flight, personally I doubt it, then I speculate she came back the same as JO did, feeling suspicious and that would have been her demise anyhow. I don't believe for one minute the RB 'worked with' Marion over a period of weeks to make these withdrawals, it doesn't seem likely, makes no sense, and let's credit Marion with a bit more sense than that - as you say she wasn't stupid. And she would have most certainly wanted to see her children and loved ones. JMO MOO