Upon motion of the attorney for the Commonwealth, preliminary hearings for persons alleged to have participated in contemporaneous and related acts or occurrences or in a series of such acts or occurrences constituting an offense or offenses may be heard jointly if jurisdiction over each person and offense lies in the same court, unless the court finds that such joint preliminary hearing would constitute prejudice to a defendant. Upon such a finding, the court shall order that the preliminary hearing for that defendant be held separately.