You have as much freedom with additional characters as you choose. I did not disclose exact numbers of those on the missions, so you can manipulate things to whatever you desire. And preliminaries or not, you should put your best writing forward. While the odds of being eliminated are 1 in 4 roughly, you should write to your best.

I set out the guidelines, but you are free to expand things as much as you want. So feel free to add what other else you want, so long it make sense, of course. Part of what is being judged is creativity.