New cat...help pleaseeee

Yesterday i had to take my friends cat in. He had to move back in with his parents, but his parents don't want the cat, so i have the cat (Flaco 1 y/o) until he finds a new place to live. I have two other cats, Miles (13 y/o neutered male) and Molly (1 y/o spayed female). I've had Molly since she was 4 months old, and she adores Miles. She always seems friendly when cats outside jump on the window. However, now that we have Flaco, she's gone completely crazy. Non stop growling, hissing, anytime he moves she goes nuts. I bought a separate litter box for him to use, and he uses a different food dish on the other side of the room. He's eaten a bit, Molly hasnt, and she hasn't used her litter in two days. My friend said Flaco was fixed, but im looking at him, and im not too sure. I don't smell any spray and i never smelled any spray when i went in his house before. Sooo, long story, sorry. If flaco's not fixed, could this be affecting mollys behavior? Or is this typical when introducing new cats?

Here is a good page on introducing cats. Most find success when the new cat is sequestered away from the resident cats. You then can start familiarizing the cats with each others scents. Also, using real vanilla extract on their chins and near the base of their tails will minimize the fact that they smell different.

Keep us posted on how you are doing.