Eloquent many-to-many-to-many - how to load distant relation easily

This isn't the complete answer but it's close. No matter how I work the data though, I can't figure out how you are coming up with cash_has. Also I'm keeping it raw SQL because I feel it would be more helpful and shouldn't be difficult to convert back to query builder. I also don't know the exact column names so you may have to fix some of those.

SELECT
    COALESCE(outlets_admin.name, outlets.name) AS outlet, 
    COALESCE(boys_admin.name, boys.name) AS delivery_boy,
    SUM(IF(cm.source_type = 'admin', amount, 0)) AS cash_taken,
    SUM(IF(cm.source_type = 'deliveryBoy', amount, 0)) AS cash_returned,
    SUM(IF(cm.source_type = 'admin', amount, 0)) - SUM(IF(cm.source_type = 'deliveryBoy', amount, 0)) AS cash_has
FROM delivery_cash_manages cm
LEFT JOIN outlets ON outlets.id = cm.destination_id AND cm.source_type = 'deliveryBoy'
LEFT JOIN delivery_boys boys ON boys.id = cm.source_id AND cm.source_type = 'deliveryBoy'
LEFT JOIN outlets outlets_admin ON outlets_admin.id = cm.source_id AND cm.source_type = 'admin'
LEFT JOIN delivery_boys boys_admin ON boys_admin.id = cm.destination_id AND cm.source_type = 'admin'
WHERE COALESCE(outlets.id, outlets_admin.id) = '2'  #  This is where you plug in your $outlet_id
GROUP BY outlet, delivery_boy

The reason you are getting an error with your query though is if you group by anything, you need to group by everything you select which are aren't aggregate columns (functions like sum, max, avg).

1. Start by using composer require illuminate/database vlucas/phpdotenv

2. create a bootstrap file to bootstrap Eloquent's connection string:

   //bootstrap.php
   <?php
   
       require 'vendor/autoload.php';
   
       use IlluminateDatabaseCapsuleManager as Capsule;
   
       $dotenv = new DotenvDotenv(__DIR__);
       $dotenv->load();
   
       $capsule = new Capsule;
   
       $capsule->addConnection([
           'driver'    => env('DB_CONNECTION'),
           'host'      => env('DB_HOST'),
           'port'      => env('DB_PORT'),
           'database'  => env('DB_DATABASE'),
           'username'  => env('DB_USERNAME'),
           'password'  => env('DB_PASSWORD'),
           'charset'   => 'utf8',
           'collation' => 'utf8_unicode_ci',
           'prefix'    => '',
       ]);
   
       $capsule->setAsGlobal();
   
       $capsule->bootEloquent();
   

3. Add environment variables!! (.env file)

4. Create a model file, you can put this anywhere you want

   //Models/User.php
   <?php
   
       namespace Models;
   
       use IlluminateDatabaseEloquentModel;
   
       class User extends Model
       {
   
       }
   

5. Use them!

   <?php 
       require('bootstrap.php');
   
       use ModelsUser;
       use IlluminateDatabaseConnection as DB;
   
       $user = User::find(1);
   
       $user2 = User::where('name', 'somename')->first();