To answer the question about Sarah, prior to Barnabas going back to 1795,[spoiler]there was a scene where Barn was (once again) throttling Julia at the Old House. Sarah appears and tells him he's a "bad man." She recites a poem to Barnabas that he had taught her in her childhood about how she must be good because the wicked are punished. She then tells Barnabas that his punishment is that he will never see her again.[/spoiler]
As for Vicki's forgetfulness after the seance and her adventure in the past, [spoiler]she has a hazy memory at best when she returns, with much of it dissipating daily. It's when she finds that portrait of Angelique in the village that she begins to remember bits of what happened.[/spoiler]
Also, at some point after 1795, I recall a scene where Carolyn and Barnabas have a conversation and Carolyn tells Barnabas [spoiler]she has to get on with her own life. He agrees, so I'm assuming they both agree to put the past behind them concerning his vampirism.[/spoiler] Still, thanks to the way it was written, it's not clear, really, that Carolyn was talking about his having held her under his spell.