Hmmm, I actually think you could go with almost anything. I don't get similar vibes from Elijah and Albie so don't think there's a style or type of name you need to stick to. Poppy and Oliver both go well with both of them. I'd probably avoid really contemporary/hippie style names but, other than that, I'd say you're good.
Elijah, Albie and ...
Adam, Arlo, Benjamin, Barnaby, Charlie, Callum, Daniel, Dylan, Elliot, Evan, Freddie, Ferdi, George, Gabriel, Henry, Hayden, Isaac, Ivan, Joel, Jesse, Kit, Kieran, Luke, Logan, Micah, Milo, Nathaniel, Nico, Oscar, Owen, Patrick, Phineas, Quentin, Quinn, Reuben, Robin, Solomon, Spencer, Thomas, Theo, Vincent, Victor, William, Wilkie, Xavier, Zachariah
Abigail, Astrid, Beatrix, Bronte, Charlotte, Cleo, Delilah, Delphi, Evelyn, Eden, Florence, Faith, Georgia, Giselle, Hannah, Harmony, Imogen, India, Joanna, Jasmine, Kathryn, Katie, Lucy, Lois, Miranda, Mika, Naomi, Nyah, Olivia, Ottilie, Phoebe, Piper, Quinn, Rosanna, Romilly, Sarah, Saffron, Tamara, Taryn, Victoria, Verity, Willow, Xanthe, Zoe, Zia