Here is a video of a few do's and don't for group posing.
Outdoor Group Portrait Posing: Portrait Photography | eHow.com
I live in east texas as you do and know that the foliage is changing colors right now and offering a great backdrop for outdoor portriats, especially around a lake. For location maybe a pier/gazebo/rustic fence with nearby colorful trees as a backdrop instead of or in addition to the lake. I guess having the shoot tomorrow does not give you much time to scout for a location but I would do it early in the day or late demending on which direction you will be shooting... I am visualizing a shoot like this and could go on and on but I am sure you get the picture :) pun intended :) Sorry if this is TMI.