When you board as the Steward for extra pillows and blankets, make each a comfy nest. Presumably they have their own seats?
Take a torch and a couple of magazines, just incase they are awake when everyone else is asleep (but don't use them until you absolutely have to). As long as they are entertained, there's a good chance you will get away with it. A bag with a few bits and bobs in it, like a soft toy from home, raisins etc. Just don't hand it all over in one go. The trick is to pull something out of the bag at the right moment. Ikea finger puppets were very useful on a longhaul flight to Oz I remember.
Accept you may not get any sleep and that it is very hard work.
If the LO really won't settle take her to the back of the plane for a toddle around, burn off a bit of energy.
Let the older one 'enjoy' the TV and headphones, even if its something you would not normally do.
So, no, sorry, no tips to get them to sleep, but remember that all you have to do is get through it. Prepare for the worst, they may well surprise you