My favorite would be [name_f]Amelia[/name_f] [name_u]Quinn[/name_u]! All three are lovely names, though, and work well with your older children’s names.
I think [name_f]Amelia[/name_f] [name_u]Quinn[/name_u] is lovely and is and feminine and classic as [name_f]Eloise[/name_f]! I prefer this spelling because it’s intuitive (for me) and then she would have her own initial.
Amelia is perfect with [name_f]Eloise[/name_f] & [name_m]Theodore[/name_m]. Plus, I just love [name_f]Amelia[/name_f] in general. It’s a fantastic balance of smart, vintage, feminine, kind & strong. I prefer [name_f]Amelia[/name_f] to [name_f]Emilia[/name_f] in general, plus you don’t repeat initials. [name_f]Penelope[/name_f] is a super cute name too, but I just prefer [name_f]Amelia[/name_f]. And [name_f]Penelope[/name_f] & [name_f]Eloise[/name_f] may be a tad rhyme-y.
First, can I say that I love your two other children’ names?! They’re darling! I love all three of your combos but I like [name_f]Amelia[/name_f] most. In my opinion, it flows best with [name_f]Eloise[/name_f] and [name_m]Theodore[/name_m] and the “A” will give her a unique initial.