Some ideas - and non A or J starting:
Cecily
Evelyn
Ursula
Sophia
Eloise
Ingrid (Indie)
Phoebe
Margot
Claire
Willow
Daphne
Serena
Sienna
Xanthe
Saskia
I really like Violet but my brain would glitch on the same endings back to back babies and just saying them in a row. But don’t think Amelia would feel left out especially as the eldest - they already feel special and often like being distinct! Also you’ll prob nickname Violet to Vy or Vio which is so different to Mila & Jules. So I’d have it as the one to beat. Keep it in top spot unless something else charms you both equally (and assuming you love Violet too).