I don’t think there’s anything wrong with choosing a popular name!
[name]Olivia[/name] is stunning. It’s popular for a reason, and I think it’s very versatile. [name]Olivia[/name], [name]Liv[/name], [name]Livy[/name], [name]Ollie[/name], [name]Via[/name], [name]Livia[/name]… I’ve even considered [name]Lily[/name], [name]Ivy[/name], and [name]Libby[/name] as nns for it, and I think a good many of them are sweet and adorable. Especially [name]Livy[/name].
I think [name]Zachary[/name] and [name]Olivia[/name] are sweet together, too.
I grew up with a very popular name ([name]Ashley[/name]), and it’s never really bothered me. I loved meeting other Ashleys. I went to small private schools most of my life, so I didn’t get overexposed to my name, which was nice. I don’t think having a popular name will kill anybody, and it seems like everyone wants something unique and unheard of. I really don’t care one way or another. Many of my favorites are quite popular, but I don’t care. They’re less popular than my name was when I was born, and I never had a problem with it. I realize that’s probably a weird opinion to have, seeing that many people on here [name]DO[/name] like less common names, but oh, well. lol. I like uncommon names as much as the next person ([name]Daphne[/name], [name]Callista[/name], [name]Clara[/name], [name]Ayelet[/name], etc. are favorites of mine, along with [name]Isabelle[/name], [name]Olivia[/name], [name]Grace[/name], [name]Charlotte[/name], [name]Lily[/name]/[name]Liliana[/name], and [name]Rachel[/name]), but I just don’t feel the NEED to use a name that is more hipster and less known than the next parent out there. My daughter may be one of the thousands of Isabelles out there, but she’ll still be MY [name]Isabelle[/name], and that’s what makes her special.
And if she’s anything like me, she’ll enjoy meeting other Isabelles/Isabellas. To me, it was almost like a game, or some secret-spy-commando mission thing. lol. It was fun being an [name]Ashley[/name]. I hope my children grow to see it the same way. If not, I’m trying to choose less popular MNs, so they can go by that if they prefer. 
But, lol, my point from all that rambling is that there is nothing wrong with [name]Olivia[/name]! In fact, it’s perfect, imo. I would love to meet siblings named [name]Zachary[/name] and [name]Olivia[/name]. On top of that, [name]Zachary[/name] isn’t all that much less common than [name]Olivia[/name]. They’re both on the top 100 used names in [name]America[/name]. If you want something a little more spunky and less common, what about [name]Liv[/name], though? I think [name]Zachary[/name] and [name]Liv[/name] are adorable together, and there’s still the sweet, girly, cute nn of [name]Livy[/name].