All of your EJBs point to a different Spring config xml file. How would they share the same Spring context if they are containing different sets of beans?
If you merge the xml files into one, at least it becomes logically possible to share a context. The Pro Spring article says the default is a different app context per ejb, but:
If this behavior is undesirable for your application, then Spring provides the SingletonBeanFactoryLocator and ContextSingletonBeanFactoryLocator classes that load singleton instances of BeanFactory and ApplicationContext, respectively. For more information, see the Javadoc for these classes