As far as I know, if you are to be a witness, regardless of whether or not you are a family member, you are not allowed in the courtroom for any of the trial. I don't believe they can even be in there for the opening statements as the statements could influence their testimony.Originally Posted by Ron x Hermione
However, being as they are to be the first witness called, and if they are witness for the prosecution, then, it is possible they would be allowed to be there for opening statements as nothing the defense could say would in theory influence their testimony.
How this would work in the Wizengamot, I do not know. We have only seen a few examples of trials. Though Mrs. Figg was not in the room until she was called in to testify. Of course, this could have been because Dumbledore wanted to keep her a secret.