I would let them sleep a little ahead of the flight. We took our kids (one of whom was 16 months, the other 3 and a bit yrs) on a 2am departure. We put them to bed as normal at around 7pm, woke them at around 11 and headed to the airport (it wasn't a long trip and we were in J). They stayed awake while in the airport and as it was a night departure we were able to get them settled fairly quickly once on board and it didn't take long after take-off before they slept again. About 4.5 hours into an 8 hour flight they woke up, but there's not really a lot you can do about that. Our home routine was similar to yours, 7pm-7am sleeping and according to their brains it was 7am where we had just left from, so time to wake up.

The sleep ahead of the airport will hopefully prevent them from being overtired at the airport where you'll inevitably have to wake them for security, boarding etc. At least if you're in J then it will be a bit more comfortable to help them settle onboard. Be prepared for the twins to be awake for the second half of the flight and pack your hand luggage accordingly

Good luck!