What is the order of the objects returned from the various scope functions? Can I rely on them being the same as the order they appear in the Quest editor (assuming no movement of objects)?

Generally it will be the order they're defined in the ASLX file. When objects move during a game though, they're moved to the end of the parent object's children (using a hidden meta-field), but not everything necessarily respects that sort order.

I would say this behaviour is undefined, so I wouldn't rely on this being the same in future versions and it may change without warning.