@Jackie591 The "Contact Airbnb" post is a large pinned post on the first page of this Help forum. Pretty hard not to see.
As far as doing a message chat- go to the Help pages on the Airbnb website. Scroll down until you see "contact Us",follow the prompts and the drop down boxes and you will eventually get to a messaging box. They sure don't make it easy or evident, but it really only takes a couple minutes to get there.
As far as why you say you want to talk to them, you needn't waste your time contacting them. You do need a separate listing for each room, unless you want to only rent all the rooms to one guest booking. If you want to be able to rent them separately, you need as many listings as rooms.
No, there is no such thing as add a room to an existing listing just because they are all in the same house.