there is a forum called goosemoose.com that caters to people with small animals for pets, especially rats. They can give you all kinds of tricks to help them to get along better but Jay_Bunny has it about right. It sometimes takes a very long time to introduce new rats into an existing cage but the best thing to do is bring everybody to a neutral area and let them get used to each other. You can use a bathtub or your bed or a couch, anyplace that you can watch them all (an extra pair of eyes never hurts either)