So what are the seating arrangements due to time booked?
I'm not totally sure what it is you're wanting to know, but maybe this will help.
There is only one Dessert Party per night. Disney has a strange way of their reservation process, and they use segmented times for their reservation process. It's guesstimated that the earlier reservation time you have, the better seating you may get. What that pattern entails, i'm not sure.
The Dessert Party generally begins about 1 hour before the Fireworks show. Despite the time your reservation is for, all people that have a reservation for that evening can arrive as soon as the Party begins...so, lets say you have a 8:45 reservation, yet they start letting people in at 8:00pm.... You can arrive at 8pm and enter then.
When entering, each table is pre-assigned, so it's not a first come first serve kinda thing. Your family name will be taped to the table you're assigned to. (so, the reservation time might be used to determine where your table may be...either way, when you get there, your table is preassigned). If you have a reservation for 2 people, you have a table for you and your guest...there are no sharing of tables. You get your own family table.
When you are seated, you are instructed that shortly before the fireworks begin, you may stand at the railing for a better view of the fireworks. You get your desserts from the tables, and the wait service will clear your table as you finish your plates. There is no limit to how many times you get desserts from the dessert table.
I hope this may clear any questions you may have. There are other little tidbits that i may not have mentioned, but can be located throughout the thread. If you have other questions, feel free to ask. i'm sure someone may have the answer for you