This is the general rule for square footage: 4 square foot per chicken inside the coop, 10 square feet per chicken inside the run. A little bigger is always better. Hope this helps!
So, if you have 9 square feet total you could have 2 maybe 3 birds, depending on size. I don't know how big your chickens get.
*Just so you know- you can use the search tab at the top of the page and search for more information about this topic. This is lots and lots of information under the "Coop & Run Design and Construction" section. There are lots of pictures of coops under that tab as well.
I have 6 in my one coop and it's about that size. They do fine and serama's are a lot smaller then my girls. Mine don't have a problem with the size of their coop. They are outside in their run 95% of the time anyways.