Best Practice To Manage Laravel 5.4 API With Existing Web

I'm working on an e-commerce project using laravel-vue for website and laravel-api for mobile application, i wanted suggestion on the best way to manage api part or the best way to implement the project

these are my thoughts on implementing this

1->using same controller for both api and web, but worried abut complex logic and scalability

public function index(Request $request) 
{
    $users = User::all();

    if ($request->wantsJson()) {
        //return json-data for mobile app
    }

    return view('agents', compact('users'));
}

2->creating separate namespace for api controllers. namespace App\Http\Controllers\Api\;

3->creating just the api using laravel and create client app using vue-cli/angular2 so that the mobile app and web app can use the same api. here concerned about SEO

any suggestions are welcome

thank you