I think they should all end in the ee sound, but have different starting letters. Love your kids' names. I think they lean unisex too, which I like!
Ideally the first vowel sound/letter will be an i and an e!
Sunnie, Casey, Bodhi and:
Juni (JOO-nee) - Inspired by the juniper tree, nature-themed like Bodhi, with a soft, unisex feel.
Jovi (JOH-vee) - Evokes "joyful" or Jupiter, with a lively, cosmic feel.
Romi (ROH-mee) - A versatile name, short for Romilly or standalone, with a modern, gender-neutral edge.
Tali (TAH-lee) - Meaning "dew" in Hebrew, it’s gentle and nature-inspired, fitting the earthy vibe.
Kiri (KEER-ee) - Evokes the kirin (a mythical creature) or a nod to nature, with a light, unisex tone.
Aerie. (AER-ie) It’s nature-inspired (like a bird’s nest high up), has a soft yet modern feel, and fits the playful, free-spirited tone of the other names.
Going on my above criteria, I am going for Kiri and Aerie, which I think pair well with each other a little bit extra to the other three siblings.