The 2 consecutive episodes I'd pick would be from the "Quentin/Beth haunt Collinwood" storyline from early 1969 - specifically where Prof. Stokes performs an exorcism on the house, and the next one where Quentin drives the family from the mansion. In just those 2 episodes, the virgin DS viewer gets to meet:
Elizabeth, Roger, Carolyn, David, Barnabas, Julia, Chris, Quentin, and Prof. Stokes.