You shouldn't have any issues. But if you want to have all 3 rooms under 1 reservation number, you may have to call Marriott Reservations and let an agent make the reservations for you. One note on keeping 3 separate reservations, you need to change one of the room reservations for anything (check-in a day later, different room type, etc.) then having 3 different reservations might make it easier to make the change without affecting the other 2 room reservations.