I think [name_f]Ella[/name_f] [name_f]June[/name_f] has a universal appeal, she’s the one I have voted for.
[name_f][/name_f]I’m one of six and I have one less name than some of my sisters. Being a name nerd, I resent this a bit and I’m in my 40’s now so I don’t think I’ll ever be maturing out of that 
[name_f][/name_f] However, my other sisters with one vs two middles have never mentioned it and likely never thought about it as it isn’t important to them. So it’s a lottery, but there is a chance[name_f][/name_f] that your lesser-middled be a bit sad that his sister got more names. Is he old enough to ask his opinion?
I wouldn’t worry about differing middles being an odd match though. You’re not in the same situation at this point and this is a different child. Good luck landing on the combination that feels right to you and for your family 
[name_f][/name_f] 