I just came back after 4 weeks in Oz with my DS who is nearly 1. We travelled Business Class, but I don't think there is that great an advantage over Economy when you travel with kids. I didn't get to relax, watch movies and sleep comfortable anyway, and even though the staff were friendly enough it is not like they took ds off our hands so we could eat a meal in peace as you hear happens to some people. I found the cot provided on the bulkhead was too small length ways for my DS who is not long for his age and so he slept on us, but when he was 8mths we went to Turkey and the cot worked really well - so it is worth a try.
On the way over I was a real martyr and didn't really ask my DH to help, but on the way back I had learnt my lesson. So number one is share the fun - though I guess with two kids both parents will be fully engaged. The flight attendants don't like you putting them on the floor (dangerous if turbulence), so when bub gets bored and fidgety the only thing to do is walk.
The main thing that was recommended to me was to take new toys so that they are engrossed more effectivley then they would be with more familiar toys.
I would recommend the parents shower in Singapore taking turns to mind the kids, if there is enough time - it will be the only 'me' time either parents get for the whole flight and will freshen them up. Take the Baby Bjorn or similar for the littley, as you won't get your stroller at Singapore or wherever you are refuelling and the Airports are huge.
Do not rely on the airline for food, I didn't thankfully, as they only had pureed food for v young babies.
Hopefully the 3 year old will like to play games and watch movies and it will be easier with the 10mth old if she is still breastfed. I don't normally breastfeed to sleep, but it works a dream on flights.
My DS has eczema which was under control before the flight but flared up under the dry warm conditions, so I would recommend moisturising the whole family to prevent skin dehydration and taking on board your own bottles of water as the service will be too slow and the portions too measly if you rely on the flight attendants.
HTH