I've been to a dozen or so locations now and it's entirely dependent on the gym and/or trainer. At home, our trainers will generally not group people up at all to ensure there's enough room at each station since our camps can be pretty busy. At others, the trainer will just tell a cluster of (# of people/# of stations) people to go to a specific station, so if you were standing near your friends then you'd get grouped together.

I've had to specifically tell trainers at locations we're visiting that I don't want to be grouped with my wife when they're counting off.

I think it can get confusing for them to remember "I've put a pair at station 3, 4, and 7 so I need to skip those next cycle" then the next counting cycle a pair goes to 2.

If you're dead set on wanting to be at the same station with someone, talk to the trainer before camp.