(We are still working on [...] the horrific idea that other people may want to sit in his favourite seat.)

Heh. Sounds familiar.

Made even worse by the fact that Amy not only wants a window seat, but (a) it has to be at the back (where the floor is higher up, so that she can actually see through the window more easily) and (b) it has to be next to me.

There are, in many busses we take, exactly four seats satisfying criterion (a), and hoping that both they and the adjacent seat are free is, well, a good setup to frustration.