My youngest is a Xanthe.
Her sisters are called Savannah and Jessica.
But there are big age gaps between all three and I have a very wide ranging taste anyway so I'm aware that none of the names are in the same 'category' as each other if you see what I mean.
I've never met another Xanthe but I see it going with either quite 'posh' names or quite 'out there' names - I don't know if one of those categories suits you? Something like:
Arabella, Araminta, Cassandra, Clarissa, Evangeline, Francesca, Georgina, Hermione, Isadora, Jacinta, Loreali, Miranda, Octavia, Seraphina, Tatiana, Vanessa
Alexander, Benedict, Christian, Elliot, Frederick, Gabriel, Hugo, Jeremy, Jolyon, Montgomery, Nathaniel, Nicholas, Orson, Quentin, Raphael, Solomon, William
Or something like:
Astrid, Aphra, Averil, Aria, Bronte, Calypso, Delphi, Effie, Fallon, Giselle, Honey, Indigo, Iris, Jessamy, Kiki, Leonie, Lyra, Mika, Mara, Nyah, Nova, Rowena, Rosina, Robyn, Saffron, Sorrel, Taryn, Tansy, Vashti, Veda, Willa, Zeryn
Arlo, Brynn, Blue, Cole, Dexter, Ellis, Flynn, Inigo, Kian, Nico, Owen, Patrick, Phoenix, River, Rocco, Talon, Titus, Victor