How can I block an apps ability to access the internet? Most have some type of built-in browser for posting on FB or Twitter that still works with safari disabled

I’m attempting to secure an iphone through the use of a parental control browser and limiting the ability of the apps to freely access the internet. The problem I keep running into is that most applications have some type of built-in browser (they can access internet even with safari deleted) that allows access to fb and other sites for the sake of promoting their products, but once you are on these 3^rd party sites you pretty much have free reign through the apps unrestricted browser. For example: I have been able to use a bible app to gain full access to a **** website with a few clicks. Is there a way to keep an app from accessing the internet through this “back door” and can you do this without affecting the functionality of the apps intended purpose?