The cadet has the 100% answer. They either know now, or they can ask their squadron. Not sure if you're a cadet or a relative/friend wanting to attend. But if you're a cadet, then you don't need to ask that question here. Just ask your AOC. If you're family/friend wanting to attend, ask you cadet.
Now, from what I remember; "My son graduated in 2012", I don't believe there was a max number, but I believe there was a need to "reserve". For my son, I know we had 8 people there. And when you say "Commissioning", I assume you mean the Night Before the graduation ceremony. The commissioning is done at the Cadet Area; while the graduation is done at Falcon Stadium. Not sure if that answered your question or not.