5yr old begs to name his sister

So I love my son with my whole heart, but he keeps saying he hates the name we picked for his newest baby sister (he already has 1 younger sister). We have been calling her Demi, but he swears up and down that it’s a boys name 🙄

He loves the name Mila and begs me anytime it’s brought up to please name her that instead of Demi.

We do love the name Mila (we were the ones to suggest it in the first place). Problem is, she doesn’t feel like a Mila. My husband and I have been calling her Demi and I like how less common Demi is than Mila right now. I know 5 baby Mila’s at the moment. I should also add that most of my family/friends prefer Mila also.

Anyways, how much say would you give to your child in naming your baby (within reason)?

Should I be considering Mila more seriously for him since he feels so strongly about it? It’s #2 on our list already