How to link two Organizations with a pair relationship?
Finally it works back to the first approach. The tipping point was to set the organization as first contact in the CiviCRM tab of the webform and then the individual contact and also change the relationship order with Organization being A and Individual being B.
Which means that I can now link two organizations or more through the same individual contact but keep everything related to the membership/contribution at the organization level and find every single needed token with related token extension.
it's a great relief.