to whom belongs distribution decision

Bonjour,

It's impossible to say unless you can state whether you have transferred the website (code, database, design) to your clients' servers. This is a key issue and is the basis of deciding if you are providing software as a service (SaaS) of just plain design, build and handover.

GPLv2:
if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have. You must make sure that they, too, receive or can get the
source code. And you must show them these terms so they know their
rights.

You cannot claim ownership over any GPL souce code, but you should be aware that the GPL licence only applies to Drupal code which you receive and then distribute. If you write custom modules, themes and don't distribute them i.e. retain them on your servers, then they are yours. Also you need to examine the terms of the contract, did the customer pay for a complete package?

There are a lot of opinions on how to deal with code transfer, and this is just my take on it, as mentioned a lot depends on your contract with the client. Clients familiar with Drupal who pay for custom design will expect to keep ownership of it.