So final update.
In TPR right now. Thank god.
1pm today got travel insurance (via flight centre I believe) to book us a flight out of USM. 4.30pm flight. And the SIN-MEL on sq217 tomorrow morning. They booked us revenue flights, so get to claim some points out of all this, Woo . They also booked Crown Plaza at changi for us.
Anyways, I did manage to speak to another KF call centre agent who advised I would only get charged the no show fees if I wanted my points back. Not going to as I don't really want to end up paying for a full fare OW fare for my trip back.
Also checked the platinum insurance pds, and it does specifically mention one way ticket does not activate the insurance. No mention of 2x one way, so you'll need to clarify with Amex travel insurance before flying.
One last mention: make sure you don't fly with Lea's than 6 months in passport. Missus flew out with 5 months left. Leaving Melb was easy. Check in agent for in MEL made a quick call somewhere and then gave the green light. As long as we travel within expiry date, it's all good. Problem arose ex-USM. Flight centre couldn't book us all on the one itinerary since it was 2-3hrs to departure ex-usm. Had to buy tickets myself and claim back later. Anywho, they [Bangkok airways] wouldn't let us check in. Took nearly 20mins to come up with a solution. We had tickets confirmed for SIN-MEL. They through-checked our luggage and we told them we wouldn't leave airport as there is transit hotel. No proof needed that we booked transit hotel (luckily since upon arrival all rooms in all 3 terminals are booked out). Other option is flight centre book BKK-SIN-MEL on one ticket, which would have been a pain, and then we fly USM-BKK via Bangkok airways.
So eventually got to SIN. Go T1 transit to check vacancy as that was the last place we hadn't checked. No vacancy. Straight to immigration to ask them if we are allowed out. It was a quick Yes, no problems. Means we can use the crown plaza reservation. So thankful we don't have to slum it in the airport for 12 hrs.
Next problem was getting our tickets for tomorrow. Went to the ticket counter inside the terminal. All good until the agent checked the missus passport. Damn! They said they need approval from Canberra to let the missus back into her own country <insert pacepalm emoji>. That just topped the trip off for me. So glad we are nearly home. I rarely miss home when I'm on holidays, but this trip was the first. Can't wait to sleep in my own bed and not need to stress about anything except for going back you work .
Thanks for all the help everyone, especially MT.