You cannot have a single document represent a reservation for more than one room or resource. Each room or resource requires their own doc for a reservation.
Why do you need them all on 1 doc? Ease of editing is about the only reason to really "need" that. However you cannot simply edit a booked reservation to make a change. You MUST create a reschedule request that the system will process once it verifies the target room/resource is available at the new dates/times.