They auto refund if you dont pay off the ticket minus something like £25 (think thats what it was last year anyway). If the deposit is £75, -£25, refund of around £50
You enter the registration details for the (upto) 6 people in on the 1st/2nd (?) page when you get in. If numbers have already been used/ are currently being used, then they will be rejected and you will not be able to move forward until you have taken them out. It will just list them as being an issue with the number/ cant find the number (something along those lines). You wont be kicked out, you will have the chance to take them out and move forward without them. It is risky as it takes up valuable time, however is doable if you have good constant communication, which also can waste valuable time.
Google docs is a great way to manage it as it can be updated live