[Teams Free] Same organization but not same emails ?

Hi,

Using Teams Free, I noticed that people from the organization are "guest" and not "members".

I wondered if this is due to differences of email inside the organization as shown https://pasteall.org/media/b/c/bccf97742fb717b8ffba546decab9713.jpg.

Is there a solution for this ? I would like that people become "members".

Thanks in advance for answers.