it doesn't descend into bitchiness, even though there are disagreements along the way.

Yes, the ghosts have always seemed aware that they're stuck with each other, and so have to make the most of it. I wonder if some of this is because the writers have been together as a troupe for so long, and it somewhat reflects their experience.

Humphrey probably sees more than realised - he does tend to be overlooked unless he complains (loudly!)

True eough.