SEARCH AND ORDER IN RELATED MODELS

Hello, i make API to show Guests with pagination. There is two tables guests and cards

guests have name, surname, email, phone and cards have numbers, balance discount and bonus

sorting by guests fields work, but i have no idea how to sort it by cards number or balance

And guest usualy have one card, but can have more than one.

    public function index(Request $request)
    {
        $guests = $request->application()->guests()->with(['cards'])->where('disabled', 0);

        if ($keyword = Input::get('q')) {
            $guests->where(function ($guests) use ($keyword) {
                $guests->whereHas('cards', function ($query) use ($keyword){
                    $query->where('number', "LIKE", "%$keyword%");
                })
                    ->orWhere("name", "LIKE","%$keyword%")
                    ->orWhere("surname", "LIKE", "%$keyword%")
                    ->orWhere("email", "LIKE", "%$keyword%")
                    ->orWhere("phone", "LIKE", "%$keyword%");
            });
        }

        $order = Input::get('o', 'id');
        $destination = Input::get('d', 'DESC');

        $guests = $guests->orderBy($order, $destination);
        
        return response()->json($guests->paginate(20));
    }