SELECT `sizes`.*
FROM `sizes`
LEFT JOIN `items` ON `sizes`.`id` = `items`.`size_id_ref`
LEFT JOIN `products` ON `items`.`product_id_ref` = `products`.`id`
LEFT JOIN `brands` ON `products`.`brand_id` = `brands`.`id`
WHERE `brands`.`name`='oneBrand'

public function getItems(){
    return $this->hasMany(Item::className(),['size_id_ref' => 'id']);
}

public function getProducts(){
    return $this->hasMany(Product::className(),['id' => 'product_id_ref'])
        ->via('items');
}

public function getBrands(){
    return $this->hasMany(Brand::className(),['id' => 'brand_id'])
        ->via('products');
}