Do you not like Eden and Clover for girls too? Eden is unisex (though maybe more often used for girls?) and Clover is usually (always?) for girls so you could have that shortlist for both sexes.
I'm not sure how it's usually spelled, but in America there is a girls' name 'Sailor' which might fit the bill for you?
Ocean, Misty and River are good ideas too.
Not to do with water but I think these girls names go well with your other children:
Amberley, Atlanta, Briar, Blair, Cleo, Coco, Devon, Danika, Effie, Echo, Fallon, Fern, Giselle, Genesis, Hadley, Harper, Ivy, Iolanthe, Journey, Jessamy, Kiki, Keltie, Luna, Lyric, Mika, Meadow, Nyah, Neriah, Opal, Oakley, Piper, Pepper, Quinn, Quincy, Rosina, Rowena, Saffron, Story, Taryn, Tansy, Vashti, Veda, Willow, Wren, Xenia, Xanthe, Zeryn, Zillah
I like Eden and Apollo best from your boys' list.
Also, how about:
Blue, Brynn, Cole, Corey, Dexter, Ellis, Flynn, Harley, Hunter, Idris, Jolyon, Jesse, Kester, Kit, Logan, Merl, Nico, Orion, Orlando, Phoenix, Robin, Rowan, Solly, Sonny, Talon, Travis, Victor