Barang.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Barang extends Model {
  
  protected $primaryKey = 'id_barang';
  
  public function kondisi()
  {
    return $this->belongsTo('App\Kondisi', 'id_kondisi', 'kondisi_id');  
  }
}

Kondisi.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Kondisi extends Model {
  protected $primaryKey = 'kondisi_id';
}

pengambilan.md

$pinjam = Pinjam::first();

$barang = $pinjam->barang;

$kondisi = $barang->kondisi->field_yang_akan_diambil;

// atau

$kondisi = $pinjam->barang->kondisi->field_yang_akan_diambil;

Pinjam.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Pinjam extends Model {
  
  protected $primaryKey = 'id';
  
  public function barang()
  {
    return $this->belongsTo('App\Barang', 'lbl_brg', 'id_barang');  
  }
}