Posibilidad de dos usuarios rellenar el mismo formulario

Welcome to the ODK forum, @Jesus_Falcon_Diaz ! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a real picture as your avatar because it helps build community!

If the users have access to the same Android device, it is possible to save a form and then resume/edit the answers in it later before submission. But there is no communication or data transfer possible between devices.

For bi-directional syncing between devices and server, you might look at ODK-X
https://docs.odk-x.org/ and https://forum.odk-x.org/ (however, setup is much more complicated than surveys in ODK).

I think on the future roadmap for ODK Central is the functionality to use Enketo to edit submissions, but there is no timeline for that.