I have Jellyfin instance open to the internet. Not many people use it besides me (and even I use it seldom for now) but I have like 3 people beside me that have tried it out.

I am not sure if there is invite capability or anything. But the way I did it is just create logins and basic passwords for my friends and family and tell them that they should change it upon first login.

As for streaming - I did watch couple of movies outside home through android app and had no issues with anything quality or connection-wise. It just worked.