Girl:
Ariadne - quite like it and one of the best matches with Persephone
Beatrice - not keen and it doesn't have the 'wow' factor of Persphone
Cecelia - quite like it
Eliza - quite like it, think you need a longer name though
Gretel - not keen and it's a mismatch imo
Heidi - quite like it but ditto to Gretel re mismatch
Liesl - dislike it
Mariella - not keen but it goes well with Persephone
Michaela - like it but total mismatch with Persephone
Boy:
Ewan - not keen
Felix - love it. Think you might need a longer, fancier name though
Gregory - not keen
Patrick - love it. How do you feel about alliteration?
Sebastian - like it. Good match
Theodore - it's ok. Good match
From other suggestions I think Electra is wonderful (if a bit bizarre!) and also love Cassandra. Antigone, Calliope, Fabian and Benedict would all go very well with Persephone imo. Ptolemy is, I think, too similar.
How about:
Araminta, Cassandra, Delilah, Elisaveta, Evangeline, Emmeline, Francesca, Georgiana, Gabriella, Henrietta, Julianna, Lavinia, Miranda, Natalia, Octavia, Ophelia, Rosalind, Rosamund, Tabitha, Veronica, Vanessa, Valentina, Xaria.
Frederick, Josiah, Maximillian, Montgomery, Nathaniel, Nicholas, Timothy, Xavier, Zachariah, Zebediah