How I would pronounce them:
Tisiphone - Tee-see-FO-nee
Alekto - Ah-lek-TO
Megaera - This one, the spelling seems a little weird to me, but going with the spelling provided, it'd be Meh-gah-EH-rah
Can't guarantee these are correct, as I have not completed my time machine in order to go back in find out (spilled coffee on the control panel again. Must rebuild from scratch). Still, a modern Greek pronounciation is better than the alternative.