Quote Originally Posted by Ron x Hermione
So the family member is not allowed to sit in the trial at all if a witness until they've given their statement. What about if the lawyer knows that the person is going to be called upon as a witness first? Can that witness, a family member, be inside the courtroom from the trial's start, because no other witness will be testify before them and taint their own evidence against the accused? They would only hear the opening statement. Is that viable and believable?
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.
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.