Redirect unauthenticated user according to their guards
  
Change your Authenticate middleware to this
  
  <?php

namespace App\Http\Middleware;

use Closure;
use Illuminate\Auth\Middleware\Authenticate as Middleware;
use Illuminate\Support\Arr;

class Authenticate extends Middleware
{
    protected $guards;

    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @param  string[]  ...$guards
     * @return mixed
     *
     * @throws \Illuminate\Auth\AuthenticationException
     */
    public function handle($request, Closure $next, ...$guards)
    {
        $this->guards = $guards;

        return parent::handle($request, $next, ...$guards);
    }

    /**
     * Get the path the user should be redirected to when they are not authenticated.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return string|null
     */
    protected function redirectTo($request)
    {
        if (! $request->expectsJson()) {
            if (Arr::first($this->guards) === 'admin') {
                return route('admin.login');
            }

            return route('login');
        }
    }
}