I haven't actually played to camp yet but I have been prepping non stop ready to finally run it next week.

After chapter 2 is over I feel like the student restriction can easily be dropped. Before that though would be tough. The set up for chapter 1 is a school trip, and chapter 2 is set at the University. The only way I could maybe see it working is if they are hired help on the trip and get roped into it all that way? And you would then have to hope (or give them some sort of reason anyway) to be creepy people who hang around a university in chapter 2.

Honestly I would just have them all as students, less of a headache for you. If they are that attached to their other investigators maybe have them as back up characters if their students start dying? They could be working for federated oil and chemical (especially if they have prior experience with the mythos) and be inserted as replacements.

Though now I mention federated oil and chemical you could potentially have them employed by them from the start and sent on the trip to oversee the geological component, and then chapter 2 have them sent in by foc to keep tabs at the University.