I have a bunch of kids, and had them relatively close together, another due soon be"H.
Its tough, but exponentially gets easier. And then the big kids help out with the small ones.
I will say that we fly quite a bit, and 16 hour flights as well. I don't look forward to it, but I wouldn't call it impossible.
I wouldn't minimize the frustration of the OP, but from a purely gashmius point of view - the Nachas is worth the effort.
Also - Ferberize!! Putting my kids to sleep takes about 2 minutes a piece, including Shema