How To Manage Source Code Access and Modular Development using Yii Framework

[codemafia]

I started out working on my website as a single developer using Yii Framework, so I don't have a very good experience on working in teams. But then the website grows, I want to hire new developers (including interns) to help me on it.I might want the new developers or interns to work on a module but without touching (or maybe reading the source code) of the core libraries (which already on top of the framework). Or maybe let the front-end developers work on the front-end aspects without seeing the entire libraries.The problem is much more like this question, and yes, a portion of the motivation is about trust. But I'm wondering if some of you can share how you manager a large team of PHP developers developing a large website on top of Yii Framework (or other popular PHP framework such as CodeIgniter, Zend Framework, etc). Or what are some good resources on managing a very large PHP project on top of PHP MVC Framework.