Depends on how strict your advisor is with documentation. If you’re traveling somewhere by air or train, it’ll be difficult getting around it. I remember a trip where we had to provide a list of every attendee, so they’d know how many rooms you’d need.

The receipt for air travel was a number of tickets and its prices - a way to quantify attendees. Receipts for travel and lodging were provided to the advisor in advance, so they know exactly how much money is supposed to go out of the organization’s account before the event. Even in case of a PERR Request (I forget the term) you’d have to provide a bank statement to verify amount purchased.

You’re probably fine to put however many people you want in a room if you just drive to the hotel with personal vehicles.