Getting out with these people before the big trip is a very good idea. There may even be people who you will decide don't belong with your group. Knowing how they act and take direction on the trail is important. You can theorize and plan all you want, but if you have someone who is determined to get lost or make other people miserable then it is a bad deal. Good Luck. Remember that safety isn't something outside the process that you sort of add on or inject...it is every part of the process and how you do it and it is all your knowledge and skills that keep you safe.