Are NKs authentic Jews? Or are they non Jews who profess to be Jewish?

Every group has their fringe elements- Neturei Karta are Judaism's. Their total number is less than 200 people,and as a group they have been put into Cherem ( form of excommunication) by Jews around the world. Are they Jewish? yep.Do they represent a tiny minority group that is rejected by the rest of the Jews world wide? Yep.