What does Callista mean?
From Greek kallistos/kallistē 'most beautiful', the superlative of kalos, from kallos 'beauty'. Kalliste was a title of the goddess Artemis; the mythological nymph Kallisto bears the same root.
What does Charisse mean?
Generally a French-styled elaboration of Greek 'charis' (grace, kindness). Some sources propose an unrelated derivation (a cherry/Latin 'ceresia' link, or a feminine of Charles), so the grace meaning is the most-cited but not undisputed.