I know it's probably not much help NOW, but I would seperate everythng that didn't need to be in contact.

You could save your scene under a new name, and delete everything excpet the characters you need to see to interact with each other.

Save the original scene again with only the props.

Once again for all background characters.

Then you can work on each element in isolation, including all parenting etc.

When you've got everything as close as possible, append each scene into one unified scene again and just do the minor fixes before render.

mo·nop·o·ly  [muh-nop-uh-lee]
noun, plural mo·nop·o·lies.
1. exclusive control of a commodity or service in a particular market,
or a control that makes possible the manipulation of prices