Depends on the situation:
If you're on good terms with one of your colleagues and know he'll be in early, invite him to GF. Then join the rest in GC shortly before the flight.
or go to GF without saying anything and meet them at boarding
Also, you'll spend most of your time together during that business trip, I don't think that a few hours apart before the flight will make any difference.
Re AUP and seats, there's the following policy in our company:
When travelling with colleagues, seat selection is at the employee's discretion.
AUP taken regardless of seniority: colleague once flew QR F while the CEO was in J.
Op-ups are not frowned upon but must be paid by the employee himself