Because the framework is designed for users new to programming, the character's names are written within the dialogue. While it is still possible to use Ren'Py's built-in definitions, extra steps would need to be taken to reformat the nametags so that they are placed correctly, as well as changing the indentation of the dialogue text. While I don't have the script that would make these needed changes, more information on indentation and nametags can be found in Ren'Py's documentation.