Taking name and other data from Joomla user db

Hello Just installed EB and a question. In my site all the events are only for registered users so I would like that when a user register he doesn't have to type his name, surname and email but these data should be pulled off the Joomla user DB.

Doing that I'm sure that one user cannot register using the name of a different user just for joke for example.

Can I do that?

I've tested the booking system. The email field is filled with the email but first and last name are not taken from the db. Also, I would need that the db taken data are not modifiable so that the user cannot register with another member name. How can I do that?

Now it's working but how can I make the first and last name unchangeable?