I'd say you have enough 'S' names. Your choices (bar perhaps Serena) are all fairly traditional (in that they've survived in the top 300ish throughout the 70s/8s/90s/00s). So, how about:
Girls - Amy, Anna, Abigail, Amber, Bethany, Charlotte, Claudia, Claire, Caitlyn, Daniella, Eleanor, Emily, Erin, Esther, Florence, Georgia, Hannah, Hayley, Hope, Isabel, Jessica, Julia, Kathryn, Katie, Lucy, Melissa, Molly, Megan, Natasha, Naomi, Olivia, Paige, Rebecca, Robyn, Rosie, Tabitha, Victoria, Zoe.
Boys - Alexander, Anthony, Benjamin, Christopher, Daniel, Edward, George, Henry, Harry, Harvey, Jonathan, James, Joshua, Joseph, Liam, Luke, Matthew, Michael, Nathaniel, Oliver, Owen, Peter, Robert, Thomas, Timothy, William, Xavier, Zachary