Am sorry but you are the wrong one here. I am Greek, you think I don't know my language?
Katherine derives from Greek AIKATHERINE which derives from the word KATHARE, 'clean', 'pure'.
EUPHEMIA derives from the words EF, 'good' and FEME, 'reputation'.
EULALIA is the one that means 'to speak well'. Anyway, you can always refer to the folowing:
In Greek, "Lexicon of Ancient Greek",
John Stamatakos
In English, "A Greek-English Lexicon", H.G. Liddell, R.Scott
(Far the best Ancient Greek to English dictionary...)
Obviously some information on this site need extra attention.
I hope I helped.