Craft Commerce: How to manage different prices with one product?
Craft Commerce support has answered to my question :


  Currently Craft Commerce can not have a stock counter that covers more
  than one variant. The default product+variant system is not designed
  for tickets. We hope to see a ticket 'Purchasable' plugin in the
  future. You can request this feature here.
  
  If you have some plugin experience, you could get around this issue
  you described with a plugin that updates the stock of other variants
  when someone purchases a variant using the onOrderVariant event. You
  would likely need to know the relationships between SKUs for the
  different variants within your plugin, and deduct the stock from the
  related variants like so:

craft()-&gt;db-&gt;createCommand()-&gt;update('commerce_variants',
  ['stock' =&gt; new \CDbExpression('stock - :qty', [':qty' =&gt; $theQty ])],
  'id = :variantId',
  [':variantId' =&gt; $variantId]);

  
  Check out the Stock Notifier plugin as it matches closely to the
  events you would need to use.