I'm assuming you're looking to do something like a hug, where each character has parts behind and in front of the other. This is one of the harder tasks in AS. I would set up my characters normally, in separate bone layers. Then I'd use the fa_meshinstance.lua layer script, and duplicate their vect...

If i put them in the same bone layer, can i still animate them separately?
I want layer 2 and 3 to be different characters.

What do i have to do to get part "D" behind part "B"?