We have had to do a lot of travel for various family things this year. And funny -- we also have been to Hawaii and Scotland/London this year too.
The flight to London is overnight, so if you can get your kids to sleep that's great -- they'll probably be pretty tired. The ergo carrier was key, I rocked Gwen to sleep in that and she slept on me on the plane. The ergo was very helpful throughout the trip; whenever she needed a nap, she could sleep on us (if a stroll in the stroller wasn't a possibility). I too did not love the bulk head bassinet.
When we went to London, we decided to keep her schedule as close to the one at home -- she goes to bed around 7 here, so there we had her go to bed closer to 11/12. And that meant she slept later in the morning. That part was amazing. But, she still didn't get as much sleep as she did at home, so we did more cat naps during the day and just went with her cues. And the longer we were there, the earlier her bedtime became, but that worked too. Our motto is to do whatever it takes when on vacation. They need extra comforting when they're in an unfamiliar place.
I too was so afraid of the trip and the return home...and it really wasn't that bad if you allow yourself to let go and be flexible. Gwen got really sick at the end of our trip to London. Her first high fever. I definitely recommend bringing an American thermometer (as we found out -- the UK's are in celcius!) and baby tylenol. We had to cross our fingers and give her some British medicine equivalent.
When you get back, it's helpful to keep baby busy with activities to get back on schedule.