pliny the elder at 2011-09-19 20:02:02:
My natural instinct would be to reduce the number of characters if possible, or at least the number of major characters.
Even if you went from 7 to 6 or 5, that might make things more managable, especially with the lack of physical space in the setting you've chosen, and make it easier for the audience to follow.
Thriller/action movies that have a similar setting such as The Rock, Executive Decision and Under Seige really focus on the core characters.
Another trick, that you have to set up, but you might want to consider is the use of "code", where two characters are talking out in the open, and the antagonist think's they're saying one thing, but they're really saying another. Shouldn't be complicated, for example a word could refer to an earlier conversation between the two, and another word entirely.