Aust east coast to Japan costs 83k Krisflyer miles per person in Business.
Aust east coast to Japan upgrade from Prem Economy to Business costs 43k Krisflyer miles per person.
Aust east coast to Japan upgrade from Economy to Business costs 65k Krisflyer miles per person.
Aust east coast to Europe costs 105k Krisflyer miles per person in Business.
Aust east coast to Europe upgrade from Prem Economy to Business costs 52k Krisflyer miles per person.
Aust east coast to Europe upgrade from Economy to Business costs 75k Krisflyer miles per person.
Personally, I would use my points on flights to EU. You would have to choose which way as your point balance can afford only 2 one-way business class seats.
Once you have a Krisflyer login (free to sign up), you could do a search on their website to find out more about the flights and taxes.
Redeem the 2 adult seats with Krisflyer miles and then ring Krisflyer to pay 10% of business class seat costs in cash for infant and attach booking with the 2 adult booking.
If I bought tickets from Sydney return to Milan (with a stop over in Singapore); when I use the points to upgrade the seats, would the upgrade apply for both the Sydney - Singapore, Singapore- Milan flights?