Oscars I know have sisters called:
Olivia, Eva, Anna, Madeleine and Isla
I also think Oscar goes well with:
Amy, Annabelle, Abigail, Alice, Alexis, Alexandra, Bethany, Bethan, Bella, Bryony, Chloe, Catherine, Darcey, Emily, Erica, Eliza, Elizabeth, Felicity, Florence, Francesca, Georgina, Georgia, Hannah, Holly, Imogen, Iona, Jessica, Joanna, Juliette, Katie, Lucy, Lily, Lydia, Louisa, Leah, Matilda, Miranda, Melissa, Megan, Miriam, Molly, Naomi, Nicole, Nia, Phoebe, Philippa, Rebecca, Rhiannon, Rosie, Sadie, Sarah, Saskia, Thea, Vanessa, Zara, Zoe