I don't know. In family law pension plans can "join" the case, and so can people like grandparents or stepparents if they are asserting visitation rights - at least in CA. I;m not sure what circumstances allow a person who is not a defendant to join a case.
Victim's Rights Advocates might speak sometimes for the victims, I think. Otherwise, they speak for themselves. If they have lawyers, it;s to help navigate through the process, but not represent them in court, unless maybe it is a restitution issue?