I don’t know if this helps you (like, at all. But hopefully it will!), but my name is [name_f]Caroline[/name_f]! I don’t go by [name_f]Caroline[/name_f] (I go by [name_f]Carly[/name_f]), but my middle name is [name_f]Gabrielle[/name_f]. You would think that the whole three-syllable thing with Car-ro-line [name_m]Gab[/name_m]-ri-elle would be strange or tiresome, but, to be honest, I didn’t really notice until we were counting the syllables of our names in school. My last name is also three syllables, and it somehow fits. Although, I supposed I’m somewhat biased, having grown up hearing the name.
Anyway, if it’s syllables you’re debating, I personally prefer one or three, but it really depends on the last name. For example, I think [name_f]Caroline[/name_f] [name_f]Isabel[/name_f] [name_m]Fitzgerald[/name_m] has a nice ring to it, as does [name_f]Caroline[/name_f] [name_f]Jane[/name_f] Fizgerald, but for a short last name like [name_m]Rhodes[/name_m], I’d say two syllables, like [name_f]Caroline[/name_f] [name_f]Hazel[/name_f] [name_m]Rhodes[/name_m].
Maybe I’m just over-analyzing this, but I can be a bit OCD with things like that. So, feel free to disagree or ignore me. 
As for the names you’ve listed, I really like the names [name_f]Hazel[/name_f] and [name_f]Isabelle[/name_f] / [name_f]Isabel[/name_f] / [name_f]Isobel[/name_f] (I can’t remember how you spelled it, but I like all spellings of that name I think.) Also, I’ve always loved [name_f]Margot[/name_f] as a name. Again, I like pretty much any spelling of it ([name_f]Margot[/name_f], [name_f]Margo[/name_f], Margeaux), but I think the way you spelled it, with a T at the end like [name_f]Anne[/name_f] [name_m]Frank[/name_m]'s sister, is better for a middle name than just plain [name_f]Margo[/name_f], which I see as more of a nickname for [name_f]Margaret[/name_f] than a stand-alone name.
Anyway, [name_f]Caroline[/name_f] is a great name, and with so many nicknames to choose from if you so desire ([name_f]Carrie[/name_f], [name_f]Carly[/name_f], [name_f]Carol[/name_f], Caddy [like Caddy Woodlawn], [name_u]Caro[/name_u], [name_f]Cara[/name_f], Liney, etc.), and even though it’s a classic, it’s not tired like [name_f]Catherine[/name_f], [name_f]Mary[/name_f], [name_f]Elizabeth[/name_f], etc. (don’t get me wrong; I love those three names! I just wish hey didn’t have that tired feel.) Again, I might be biased, as it is my name. But since I go by [name_f]Carly[/name_f], and so many people probably don’t even know that my name is actually [name_f]Caroline[/name_f], I almost feel like it isn’t my name at all.
I told myself that I wouldn’t talk your ear off, but then I started rambling. Sorry. [name_f]Hope[/name_f] you find a good middle name!
I also love [name_f]Caroline[/name_f] [name_f]Margot[/name_f] and [name_f]Caroline[/name_f] [name_f]Audrey[/name_f].
I think I"m over-thinking again.