Update stock with php

This is a bit of custom work so I don’t expect the dev to answer, maybe the community? Thanks for any help I could receive.

In my Woocommerce store, products are set as simple, but I use WS Form to add attributes to the product/order.

https://dev.biancoviaggi.com/viaggio/viaggio-a-medjugorje-in-pullman-il-29-03-2024/

We sell travels packages. When a user purchase a product, the quantity decrease to 1. But if they’re a group of 4 travelers, the correct approach for our use case should be to decrease the stock of 4 (total number of people partecipating).

I tried this snippet that althought it correctly updates the stock quantity on purchase, it makes the wrong calculation:

add_action('woocommerce_checkout_order_processed', 'adjust_stock_based_on_travelers_checkout', 10, 1);

function adjust_stock_based_on_travelers_checkout($order_id) {
    $order = wc_get_order($order_id);

    foreach ($order->get_items() as $item_id => $item) {
        // Passeggeri totali means "Total passengers"
        $passenger_total = wc_get_order_item_meta($item_id, 'Passeggeri totali', true);
        $passenger_total = intval($passenger_total);

        if ($passenger_total > 0) {
            $product = $item->get_product();
            if ($product && $product->managing_stock()) {
                // Correctly decrease the stock
                $new_stock = wc_update_product_stock($product, $passenger_total * -1, 'decrease');
                
            }
        }
    }
}

I’m not sure where I found this similar approach that I applied, but probably there’s a better way to start this