Each app has it's own node, so if you want to deploy an additional app, you require an additional node.
You could build the functionality in the same app, perhaps separated by user roles, but this is not a long term sustainable solution.
By default you cannot have several applications deployed into the same cloud node.
But you have also the option to deploy the application to a private cloud (if your licence permits). It would be considerably more work you need to take over, however you would be free to scale the system as needed. With this you could have bigger systems that can host large (combined) applications with a shared domain model and even add more power as needed. Or you could have even smaller (or more price efficient) cloud nodes than available now in the regular Mendix Cloud Options(AWS). But please consider the additional administrative overhead for provisioning of these infrastructure services.