Having two skeletons interact is no different than working on a single animation, you just need to make the animations play together. For example if I wanted to create an animation where one character rides on the back of another I would pose both characters just as I do with a single character in rough steps. Then once those rough steps are done I would hide the character riding on the back and finish the animation on the other character. Once that is done, unhide the hidden character and make it's animation match the first one.
Same applies for a 5 second runtime, there is nothing different about it, you just have more elements on screen and the animation is longer. Personally I would do something like this at the end where I already have basic walk, run, jump etc. animations I can then bring in and tweak so they fit the cutscene.
Making videos for how to set things up at runtime is something we will eventually do, but we still want the runtimes to be locked down a bit more. Also this is something Nate would be doing and he is currently very busy adding all the features.
