We assign your project to a senior iOS engineer and a team of developers to work with him/her. You can communicate with that project manager and share all the information with him or her. The concerned project manager will convey your requirements to the developers and you can get a customized app. Moreover, you can talk to the developers as well and share your requirements with them too. And ask which development platform they are using. This way you can contact the concerned person directly and reduce the communication gap. The developer coordinates with the manager and makes the changes in the app as per needs. So, yes you can talk to the iOS developers working on your project and share your requirements and updates you want in the app.