I think Miles is perfect! I agree with @LoloTen that id avoid having shared initials (e.g. Sonny and Spencer) and Ollie and Ellis are a bit too similar to Ayla. Oakley is good too but maybe a bit of a different vibe to your other kids. Finn would also work great though!
Some more ideas if you want just in case that doesn't feel right:
Archie - “genuine, bold”
Ben / Benny - “son of the right hand”
Bodhi / Beau - “awakening, enlightenment” / “handsome”
Emmett - “truth; universal”
Emrys - “immortal”
Evan - “God is gracious”
Ezra - “help, helper”
Felix - “happy, fortunate”
Fletcher - “arrow maker”
Flynn - “son of the red-haired one”
Frankie - “free one”
Hugo - “mind, intellect”
Jasper - “treasurer; bringer of treasure”
Joel - “Yahweh is God”
Jude - “praise”
Leo - “lion”
Levi - “joined, attached”
Luca - “bringer of light”
Louie / Louis - “famous warrior”
Max - “greatest”
Micah - “who is like God?”
Milo - “merciful”
Noah - “rest, comfort”
Noel - “birth; Christmas”
Otis - “wealth, fortune”
Otto - “wealth, prosperity”
Owen - “young warrior; well-born”
Robin - “bright fame” (also a bird)
Rory - “red king”
Ryan - “little king”
Rowan - “little red one” (also a tree)
Teddy / Theo - “gift of God”