Oh, that's a good question! I did the same and cancelled one for my dh and ds, as I had accidentally put them on for the A&E FP. They are ok not rebooking during that time slot and will something to do. (Because it was too big of a pain for me to deal with calling and adding a 3rd for them). But When our 3rd is up, will they let my dh and ds rebook another along with us if they only had 2 booked and used?