My initial response is that you’re asking a bit too much and that you should spend another year or so accumulating points and then try for 2021. This is my thinking…
Your Westpac Altitude points will convert to 73,333 FF points. With just about every FF programme you need well over 100,000 points for one one-way business-class redemption.
The one window of opportunity you may have is with Asia Miles, because you’ll need as little as 85,000 points for a one-way redemption in Business. Asia Miles also allows you to purchase points at a rate of USD60 per 2000 points. You’ll need to purchase 12,000 points, for USD360 (which comes to A$520). On top of that, you’ll need to pay something like $300 in taxes and charges for the redemption, so you’ll be paying well over $800 in extra points, taxes and charges for one one-way business class flight. And you’ll have to pay money for the other three flights.
So you’ll only have enough points for one flight. If you wait another year and put your newfound point hacking skills to good use, within 12 months you may well have enough points to fly the two of you return.
As for your second question about availability – yes, it really does depend on route, airline and day of week. The bad news is that of all the FF programmes you can transfer your Altitude points to, Cathay Pacific availability (via Asia Miles) is probably the worst. I booked an Asia Miles redemption in Business class to Europe for my wife and me a couple of months ago, and it literally involved waking up at 3am to grab the reward seats minutes after they were released! That’s the best way to go about things with Asia Miles; with other programmes such as KrisFlyer it’s easier and there’s more availability, but at the cost of requiring more points.
What you have going for you is flexibility. Again with Asia Miles/Cathay Pacific, look to flying into Milan – in my experience there’s more availability into Milan than just about any other city in Europe (there’s also great availability into Manchester if you get desperate).
I hope this helps but the bottom line is that you’ll either need to pay for most/all of your flights, or wait another year.