Legal Question in DUI Law in California

Courtrooms are open to the public.

Yes, you may attend. The only reason you would be excluded is if you were a subpoenaed witness and it was during the testimony of other witnesses.

Court proceedings are open to the public. You can sit and watch, not participate. If he is in custody, you will not be allowed to talk to him or approach him. You could try to talk to his attorney if he has one. If he doesn't, he should hire one, preferably before the court hearing, so the attorney can seek bail reduction or OR release. If you or he is serious about hiring counsel to help in this, and if this is in SoCal courts, feel free to contact me