Your girls are wonderfully named and your list is beautiful 🩷
From your favourites I absolutely love as a sibling for your kiddos Clementine, Agatha, Theodora, Penelope & Calliope as first names. I think Juniper & Bluebell would make lovely middle names that feel in keeping with the fun alliteration of MM’s name and the nature theme of SW’s name. I think something like Agatha Bluebell or Calliope Bluebell would be gorgeous.
Suggestions:
Persephone, Florence, Delphine, Romilly, Odette, Cosette, Elodie, Rosamund, Amelie, Tulip, Tallulah, Heidi, Ingrid, Willa, Arabella, Bronwen & Paloma.
Concerning your boys I love Reuben & Jasper both these choices are distinguished with a classic pan European feel. They feel very in keeping with your girls names. So I think you’re off to a great start despite finding boy names trickier.
Suggestions:
Felix, Tobias, Caspar, Gideon, Simeon, Vincent, Victor, Gabriel, Rhodes, Finnian, Phineas, Caspian, Beau, Rome, Ronan, Adair, Ambrose, Leon,
Ives, Maxim, Lior, Leopold, Julian, Julius, Edmund, Pascal, Magnus, Wilfred, Oscar, Otis, Flynn + Elio.