I quite like Evie but I think I would use Eva, Evelyn or Evangeline and use Evie as a nickname.
I'm not keen on Siobhan. It seems quite dated. Unless you're in Ireland in which case I have no idea if it's dated or not. But I would assume an English Siobhan to be a 70s-90s baby.
I also wouldn't worry about matching with Hermione but, if you wanted a longer, classical, slightly unusual name, how about:
Aurelia, Antonia, Araminta, Arabella, Ariadne, Beatrice, Cassandra, Clarissa, Carolina, Christabel, Elizabeth, Francesca, Felicity, Georgina, Henrietta, Isadora, Jacinta, Juliette, Katerina, Liliana, Lucinda, Lorelai, Larissa, Miranda, Marianne, Natalia, Natasha, Ophelia, Octavia, Persephone, Pandora, Rosaline, Rosemary, Sylvia, Seraphina, Susannah, Tatiana, Vanessa, Victoria, Xanthe
Names which I associate with Evie:
Annie, Amber, Abbie, Bonnie, Chloe, Connie, Cleo, Daisy, Darcey, Ellie, Emily, Elsie, Edie, Esme, Erin, Eden, Effie, Freya, Gracie, Hollie, Heidi, Isla, Ivy, Iris, Jasmine, Kayla, Katie, Kitty, Lily, Lucy, Layla, Lola, Leah, Molly, Millie, Mia, Maia, Maddie, Nia, Poppy, Phoebe, Ruby, Rosie, Sophie, Sienna, Sylvie, Summer, Scarlett, Tilly, Tia, Thea, Willow, Zoe
Names which I associate with Siobhan:
Anita, Annette, Amy, Alison, Ashleigh, Asha, Angela, Bryony, Billie, Claire, Carly, Caroline, Courtney, Danielle, Denise, Deborah, Emma, Erica, Fiona, Hannah, Helen, Hazel, Jennifer, Joanna, Joanne, Jane, Jade, Joy, Jocelyn, Jacqueline, Julia, Karen, Kimberly, Kayleigh, Lisa, Lindsay, Lynne, Louise, Louisa, Melanie, Melissa, Maria, Miriam, Michelle, Nicola, Nicole, Naomi, Philippa, Rebecca, Rachel, Ruth, Robyn, Sarah, Samantha, Stephanie, Sian, Sinead, Suzanne, Tiffany, Tanya, Theresa, Vivienne, Valerie, Wendy, Zoe