Hello
@Happy,
thank you for your question and joining our community.
As you rightly assumed it is n ot possible to start the marriage process unless he has the legal right to be in Greece (e.g. being a registered asylum seeker). Once this is done he will need to obtain a passport from his native coutry.
I hope we could address your question, if you need further guidance please do not hesitate to reach out to us.
Best regards,
Nilab