What does Eleni mean?
Modern Greek form of Helen/Helene. The etymology is uncertain: most often linked to Greek 'hele' ('torch') or a root meaning 'shine/bright', with some scholars instead proposing a connection to the moon or a pre-Greek word of unknown meaning. The 'torch/bright light' reading is traditional but not settled.
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.