There were two episodes involving "trials" in which several ghosts were summoned to act as a "jury", one in 1968 and one in 1897 I think. Each of these episodes included at least 7 or 8 people.
Also the very last episode before 1841PT took over included a bunch of people -- Judge, Gerard, Quentin, Julia, Barnabas, Angelique, Trask, Joan Bennett (Flora and Elizabeth), Daphne, Desmond, Leticia, Prof Stokes, Judah's head and at least 1 or 2 extras taking on roles at Quentin's execution. By the way I'm counting the opening recap as part of the episode, as this is when the whole scene at the execution chamber takes place, I think.