What a lovely sibset! [name_m]Theodore[/name_m], [name_m]Maximilian[/name_m] and [name_f]Louisa[/name_f] are all gorgeous. I love the grand, almost classical feel, balanced with such sweet, wearable nicknames. I can definitely see why you’re finding it hard to choose a fourth name that feels just right!
Of your current options, I think [name_m]Frederick[/name_m] is wonderful with your other children’s names. I understand your hesitation about [name_f]Fred[/name_f] and [name_m]Freddy[/name_m] rhyming with [name_m]Teddy[/name_m], though! I do think [name_m]Frederick[/name_m] is a name you can use in full, especially since you already tend to call [name_f]Louisa[/name_f] by her full name. [name_m]Freddie[/name_m] might be a natural nickname for some people, but it isn’t inevitable, and you could always introduce him as [name_m]Frederick[/name_m] and see what develops, or you could maybe use [name_f]Ricky[/name_f] as a nickname. I also really like [name_m]Julius[/name_m] for you! It has that grand, [name_m]Roman[/name_m] feel of [name_m]Augustus[/name_m] and [name_m]Aurelius[/name_m], but it’s a little less expected than [name_m]Alexander[/name_m]. [name_m]Julian[/name_m] is lovely too, but I can see what you mean about it feeling a little understated beside your other names. [name_m]Julius[/name_m] has a bit more character and presence to me. I wouldn’t rule out [name_m]Alexander[/name_m], either. I think a name being familiar isn’t necessarily a bad thing when you love the sound of it so much. As for [name_m]August[/name_m] or [name_m]Augustine[/name_m] , I can understand feeling hesitant after using [name_m]Augustus[/name_m] as a middle name for [name_m]Theodore[/name_m]. Personally, I would probably lean away from either, simply because they feels quite close to [name_m]Augustus[/name_m], but I don’t think it would be outrageous to use [name_m]Augustine[/name_m] or [name_m]August[/name_m] if you genuinely loved it. Families reuse names and honour names in all sorts of ways!
And I actually love [name_m]Constantine[/name_m] for your family. I don’t think it’s too much alongside [name_m]Theodore[/name_m] and [name_m]Maximilian[/name_m] at all; it fits the classical, substantial feel of your boys’ names beautifully. [name_m]Constantine[/name_m] also has some lovely nickname possibilities, such as [name_f]Connie[/name_f] or [name_m]Tino[/name_m], if either appealed to you.
A few other names that came to mind were:
[name_m]Atticus[/name_m] ‘Kit’
[name_m]Ambrose[/name_m] ‘Bram’
[name_m]Anthony[/name_m] ‘Ant’
[name_m]Barnaby[/name_m] ‘Barney’
[name_m]Benjamin[/name_m] ‘Benji’
[name_m]Callahan[/name_m] ‘Cal’
[name_m]Christopher[/name_m] ‘Chris/Kit’
[name_m]Cassian[/name_m] ‘Cass’
[name_m]Clarence[/name_m] ‘Lance’
[name_m]Dominic[/name_m] ‘Dom’
[name_m]Evander[/name_m] ‘Evan/Andy’
[name_m]George[/name_m] ‘Georgie’
[name_m]Gilbert[/name_m] ‘Gil’
[name_m]Lucian[/name_m] ‘Lucky/Luci’
[name_m]Leander[/name_m] ‘Lee/Andy’
[name_m]Larence[/name_m] ‘Laurie’
[name_m]Nathaniel[/name_m] ‘Nate’
[name_m]Nicholas[/name_m] ‘Nicky’
[name_m]Raphael[/name_m] ‘Ralph/Ralphie’
[name_m]Rafferty[/name_m] ‘Rafe’
[name_m]Sebastian[/name_m] ‘Seb/Bash’
[name_m]Vincent[/name_m] ‘Vinnie’
[name_f]Hope[/name_f] this helps!