Hi lightspeed,
I don't know if this is going to help any, I have several different voices and I use them to read a book, each voice I had was a different character in the story.
The first thing I do want to mention is, it was a real undertaking job, a lot of hard work, and very time-consuming.
I imagine this could be adapted to video, though I don't have a lot of experience in this, I've only taken on the challenge of doing audio books.
Here is a short description of how I was able to accomplish this, I had my first voice read the entire story, I had the second voice read the entire story, and so on.
I used a program called Goldwave, IN GOLDWAVE you have the ability to have many different wave files open at the same time.
so starting with the first voice that I used to record the entire story, When it got to a point where the second voice was supposed to be speaking.
what I did was cut and paste that voice from the second voice wave file and paste it into the first wave file, I continued to do this for all the voices.
Also while I was listening to the story and cutting and pasting the voices, that gave me the ability to remove from the wave file things like, "and Jackie said", etc., from the story line.
how I was able to keep track of all the different voices with the different characters in the story was, I named each wave file the name of the character in the story.
Sincerely, and I hope I was able to help just a little bit.
C load.