I wanted to how hard it was to switch out people in my party. I have a Cat 2 booked for December 2010 for 5 people and even though it's a long way off, there is a chance that my mother may be too ill to go. While we hope that's not the case, she wanted to know if it would be hard to have her sister,my Aunt, to go instead. How much advance warning does DCL need? Thanks!