Yes that is exactly the case. Often judges do order witnesses who express reluctance to testify into custody so that they can be sure that they will show up for the trial.
This is extremely rare in the US judicial system, and prosectors tend not to like take cases where the victim or a key witness is no longer willing to testify.
Yes, judges and lawyers for both parties in a case can legally compel witnesses to show up and testify, but doing so tends to damage the credibility of the witness, which can be fatal for their testimony.
