what are the non-existing members here in the forums?
Are they banned?

Yes, when it says non-existing they are banned.

not always some people just like to put that as a picture i beleive there is an organization for that
But just look carefully at the color the real banned are red
The fake banned are bith orangisch

Also worth noting that real non-existing text is highlight-able. The fake one is not.

Or you can check the ban list to see if they are banned and how long they are banned.