I have done the class twice. The class takes place before the bakery opens so there are only students and a couple of staff members. They rearrange all the tables for the class and the entire class is done while sitting at a tables. Everything you need is at your table or brought to you. Some students stand up to pour the icing on the cake to get a better view of what you are doing, but it can also be done sitting.
The first class I did was the regular Mickey hat. The Instructor invited 1 person from each pair to bring their cake to the front to add writing on the back. The instructors works at a standing height table. For the second class, I did the Santa Mickey hat and we did everything at our own tables.
There is a mid class break where everyone can get up and wander around and look at the treats they are setting up for the day. Or you can just stay at your table.
I would recommend calling them and letting them know that you will be using a wheelchair so you can be seated where you have enough space. The tables are arranged so everyone has a good view. The people on the sides have more space behind them then the ones against the wall.