How to create a Web application from React-Native code with little bloodshed?

Question

Mobile development

The application has not yet been written. I have experience in MVC, but no experience in React.
The end goal should be:

• Client application for iOS/Android
  
• Web application
  

The bottom line is that a web application should have additional functionality.
That is, some modules that will be written under React-Native should not work (for example, access to the camera, or something else), but some are added: styles for wide screens, additional modules (admin module).
In total, there are two questions:
1. Which existing React-Native -> WebApp method to take (there are several of them)
2. How best to organize the code in order to connect certain modules (component, css) depending on the platform.