Goth: Relates either to medieval times or means "an uncivilized person" or "a person without culture". The Goth name in general has some resemblance, as well. The family seems to be the oldest (making it "medieval").
Mortimer: In French, "mort" means death. Could also mean "still water".
Cassandra: Of Greek origin it means "One who helps mankind" or "She Who Entangles Men". In Greek myth, Cassandra was a Trojan Princess who had been given the gift of prophecy by Apollo.
Alexander: Means "defending man". Alexander the Great was the leader who created an empire through Greece, Egypt, Persia, and parts of India.
Spencer: From a surname that meant "dispenser of provisions", derived from Middle English spense "larder, pantry".
Kim: At the present it is usually considered a short form of Kimberly, but it in fact predates it as a given name. The author Rudyard Kipling used it for the title hero of his novel Kim (1901), though in this case it was short for Kimball.
Lewis Medieval English form of Louis.
Eric: Means "ever ruler", from the Old Norse name Eiríkr, derived from the elements ei "ever, always" and ríkr "ruler, mighty".
Vivian: From the Latin name Vivianus, which was derived from Latin vivus "alive".
Alice: From the Old French name Aalis, a short form of Adelais, itself a short form of the Germanic name Adalheidis.
Dennis: Usual English, German and Dutch form of Denis.
Olivia: May have been based on Oliva or Oliver, or directly from the Latin word oliva meaning "olive".