Not sure I understand this completely, but you can make a reservation, and then try to book a second one for the same dates (additional room) and if they are booked up you could go on the wait list. Is that what you mean?
You only go on the wait list if they don't have room to take a reservation. And yes, you can have two reservations at one place at the same time for different rooms.
Does this answer your question, or am I completely misreading it?