Along similar lines to Hettie, Mila and Mailie:
Allie, Alix, Alys, Arwen, Astrid, Aria, Ayla, Amy, Ada, Anya, Bailey, Bella, Bonnie, Bessie, Betty, Betsy, Billie, Chloe, Clara, Cara, Carla, Casey, Connie, Cassie, Callie, Carrie, Darcey, Dana, Demi, Emmie, Ellie, Ella, Eva, Evie, Edie, Esme, Elsie, Elise, Elsa, Erin, Eden, Etta, Enya, Effie, Ellis, Farrah, Florrie, Faye, Freya, Fleur, Faith, Grace, Gracie, Gia, Gina, Hattie, Harper, Hayley, Harley, Hadleigh, Iris, Isis, Izzy, Josie, Jodie, Jayla, Jada, Katie, Kitty, Kayla, Kyla, Kyra, Kia, Kaya, Kya, Kayleigh, Kelsey, Keeley, Kenzie, Kiki, Keltie, Lucy, Lily, Layla, Lyla, Lyra, Luna, Lola, Lisa, Laiba, Livia, Leah, Lacey, Lexie, Libby, Lottie, Lois, Maisie, Martha, Mia, Maya, Mya, Molly, Millie, Mina, Mira, Marnie, Marcie, Macey, Miley, Marley, Mimi, Maddie, Nia, Noa, Nyah, Nora, Pippa, Poppy, Polly, Peggy, Phoebe, Piper, Pepper, Rosa, Rosie, Roxy, Ria, Romy, Ruby, Ryleigh, Sophie, Skye, Sadie, Sydney, Sylvie, Susie, Sally, Tia, Taya, Thea, Taylor, Tara, Tessa, Wendy, Zoe, Zia.
Also, your other children's names sound like you might have some Irish or Gaelic/Celtic blood somewhere?
Names like Ciara, Cerys, Carys, Celyn, Iona, Eilidh, Ailsa and Kirsty could go well?