We have a
Juniper Elizabeth
Abel Rupert
Looking what to name our third. I’m liking Harris and Benjamin for a middle. Any more suggestions for us? This is what we have so far… Surname begins with B and two syllables.
Jesse Harris
Linus Benjamin
Bram Harris
Rufus Benjamin
Robin Harris (Robbie)
Asher Benjamin
Linden Harris
[name_u]Juniper[/name_u], [name_m]Abel[/name_m] and [name_m]Linus[/name_m] is a delightful set 
I also really like [name_m]Bram[/name_m], [name_u]Robin[/name_u] and Rufus!!
I’ll throw in the suggestions of:
[name_u]Juniper[/name_u], [name_m]Abel[/name_m] and…
[name_u]Clyde[/name_u]
[name_u]August[/name_u]
[name_m]Evander[/name_m]
[name_u]Thaddeus[/name_u]
[name_m]Oswin[/name_m]
[name_m]Fergus[/name_m]
[name_m]Edwin[/name_m]
[name_u]Sasha[/name_u]
[name_u]Quentin[/name_u]
[name_m]Lorcan[/name_m]
[name_u]Beck[/name_u]
[name_u]Ira[/name_u]
[name_f]My[/name_f] favorites are [name_u]Jesse[/name_u] [name_m]Harris[/name_m] & [name_u]Linden[/name_u] [name_m]Harris[/name_m]
[name_m]Hi[/name_m] there.
[name_u]Juniper[/name_u] & [name_m]Abel[/name_m] are lovely!
Here are my thoughts for #3:
[name_u]Jesse[/name_u] Harris-I don’t mind this. [name_u]Jesse[/name_u] is a name that I wished I like more, since I love the chill cowboy vibe that it gives. I just don’t like the sound that much though. It does fit in well w/your crew, & is well known but not over done.
[name_m]Linus[/name_m] Benjamin-Linus is so so adorable. A little geeky, but I think just on the cusp of not too geeky. It’s just charming.
[name_m]Bram[/name_m] Harris-This is okay. It’s a little bland, & I like it better as a nn for [name_m]Abram[/name_m]. But that’s too close to [name_m]Abel[/name_m].
[name_m]Rufus[/name_m] Benjamin-I don’t know. It’s kind of interesting, but just feels goofy to me.
[name_u]Robin[/name_u] Harris-This is not usually a name that I like that much, but it does have pretty (but not too girly) & calm energy. And [name_u]Juniper[/name_u], [name_m]Abel[/name_m] & [name_u]Robbie[/name_u] are unexpected & kind of cute.
[name_u]Asher[/name_u] Benjamin-Asher is really handsome. It’s a good balance of outdoorsy ruggedness & gentle artist type. [name_u]Perfect[/name_u] w/Juniper & [name_m]Abel[/name_m]. Perhaps a bit more common than the rest of the list if that bothers you.
[name_u]Linden[/name_u] Harris-I don’t know. It’s not my cup of tea. It’s too close to the ultra trendy [name_u]Landon[/name_u] & [name_u]Logan[/name_u].
A few other ideas that you may like:
[name_u]Arlo[/name_u]
[name_u]Alden[/name_u]
[name_u]Bennett[/name_u]
[name_m]Clark[/name_m]
[name_m]Desmond[/name_m]
[name_u]Ellis[/name_u]
[name_u]Elliott[/name_u]
[name_u]Elias[/name_u]
[name_u]Emmett[/name_u]
[name_m]Ferris[/name_m]
[name_u]Finn[/name_u]
[name_u]Ira[/name_u]
[name_m]Louis[/name_m]
[name_u]Levi[/name_u]
[name_u]Milo[/name_u]
[name_m]Otis[/name_m]
[name_u]Owen[/name_u]
[name_u]Rowan[/name_u]
[name_m]Silas[/name_m]
[name_u]Shiloh[/name_u] 
[name_u]Shaw[/name_u]
[name_m]Simon[/name_m]
[name_u]Tristan[/name_u]
[name_m]Thatcher[/name_m]
[name_m]Zev[/name_m]
[name_f]Hope[/name_f] this helps. 
I love [name_m]Linus[/name_m], [name_m]Bram[/name_m], & [name_u]Asher[/name_u]! Both middles are great.
More ideas:
[name_u]Finn[/name_u]
[name_u]Lyle[/name_u]
[name_u]Connor[/name_u]
[name_u]Noah[/name_u]
[name_m]Matthew[/name_m]
[name_m]Caleb[/name_m]
[name_u]Corbin[/name_u]
[name_u]William[/name_u]
[name_m]Alexander[/name_m]
[name_u]Oliver[/name_u]
[name_m]Zachary[/name_m]
[name_m]Josiah[/name_m]
[name_u]James[/name_u]
[name_u]Walter[/name_u]
[name_m]Wayne[/name_m]
[name_m]Ivan[/name_m]
[name_u]Logan[/name_u]
Oh my [name_m]Linus[/name_m] [name_u]Benjamin[/name_u]
I adore [name_u]Robin[/name_u] [name_m]Harris[/name_m]
[name_f]My[/name_f] favourite is [name_m]Bram[/name_m] [name_m]Harris[/name_m], followed by [name_m]Rufus[/name_m] [name_u]Benjamin[/name_u], [name_u]Jesse[/name_u] [name_m]Harris[/name_m] and [name_u]Asher[/name_u] [name_u]Benjamin[/name_u].
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_m]Wilson[/name_m] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_m]Silas[/name_m] [name_u]Benjamin[/name_u]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Nolan[/name_u] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Landon[/name_u] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Vaughn[/name_u] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Holden[/name_u] [name_u]Benjamin[/name_u]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_m]Felix[/name_m] [name_u]Benjamin[/name_u]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Elias[/name_u] [name_u]Benjamin[/name_u]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_m]Jethro[/name_m] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_m]Fletcher[/name_m] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Walter[/name_u] [name_u]Benjamin[/name_u]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Dane[/name_u] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_m]Otto[/name_m] [name_u]Benjamin[/name_u]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_m]Josiah[/name_m] [name_m]Harris[/name_m]
[name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f], [name_m]Abel[/name_m] [name_m]Rupert[/name_m] and [name_u]Grey[/name_u] [name_u]Benjamin[/name_u]
[name_f]My[/name_f] favourite would be [name_u]Juniper[/name_u], [name_m]Abel[/name_m] and [name_m]Rufus[/name_m]! [name_m]Linus[/name_m] and [name_m]Bram[/name_m] are also good options
[name_m]Linus[/name_m] [name_u]Benjamin[/name_u]! Oh my, so handsome!
Others that come to mind:
[name_m]Calvin[/name_m]
[name_m]Clark[/name_m]
[name_m]Hugh[/name_m]
[name_u]Leo[/name_u]
[name_u]Sloan[/name_u]
[name_m]Tobias[/name_m] (Toby)
I also love [name_u]Robin[/name_u], but not [name_u]Robbie[/name_u].
Either [name_m]Linus[/name_m] [name_u]Benjamin[/name_u] or [name_m]Rufus[/name_m] [name_u]Benjamin[/name_u] for me. Though I lean way more towards [name_m]Linus[/name_m]
[name_u]Robin[/name_u] [name_m]Harris[/name_m] or [name_m]Bram[/name_m] [name_m]Harris[/name_m] are good fits
[name_m]Rufus[/name_m] is fantastic, quirky and cool. It goes brilliantly with [name_u]Juniper[/name_u] and [name_m]Abel[/name_m] too!
Other ideas:
[name_m]Bastian[/name_m]
[name_m]Otis[/name_m]
[name_m]Phineas[/name_m]
[name_u]Calloway[/name_u]
[name_u]Kit[/name_u]
[name_u]Ezra[/name_u]
[name_m]Cyrus[/name_m]
[name_m]Otto[/name_m]
[name_u]Fox[/name_u]
[name_m]Hawthorne[/name_m]
[name_u]Rex[/name_u]
[name_m]Orson[/name_m]
[name_m]Magnus[/name_m]
[name_m]Felix[/name_m]
[name_m]Caspar[/name_m]
[name_u]Gus[/name_u]
[name_m]Rafferty[/name_m]
[name_m]Lucian[/name_m]
[name_m]Elio[/name_m]
[name_m]Tobias[/name_m]
[name_u]Remy[/name_u]
[name_m]Silas[/name_m]
[name_u]Rory[/name_u]
[name_u]Sullivan[/name_u]
[name_m]Miro[/name_m]
[name_m]Oscar[/name_m]
[name_u]Levi[/name_u]
[name_u]Darcy[/name_u]
[name_m]Hugo[/name_m]
[name_u]Rafe[/name_u]
[name_u]Jesse[/name_u], [name_m]Linus[/name_m], or [name_u]Asher[/name_u]. I think all three would sound great with your sibling set.
[name_m]Rufus[/name_m] [name_u]Benjamin[/name_u]!
So handsome and goes so well with his siblings’ names.
Congrats!
Firstly I love your children’s names especially [name_m]Abel[/name_m]. [name_m]Abel[/name_m] is sooooo handsome 
From your list I love [name_m]Bram[/name_m] [name_m]Harris[/name_m], [name_u]Robin[/name_u] [name_m]Harris[/name_m] & [name_u]Asher[/name_u] [name_u]Benjamin[/name_u].
I think my favourite from this three is [name_m]Bram[/name_m]. [name_m]Bram[/name_m] is sweet upbeat and fun he has the same vintage quality of [name_u]Juniper[/name_u] & [name_m]Abel[/name_m] making an overall lovely sibling set.
Also [name_m]Bram[/name_m] [name_m]Harris[/name_m] sounds like a very cool jazz player I love it!
I think [name_m]Linus[/name_m] [name_u]Benjamin[/name_u] or [name_u]Asher[/name_u] [name_u]Benjamin[/name_u] sound great with [name_u]Juniper[/name_u] [name_f]Elizabeth[/name_f] and [name_m]Abel[/name_m] [name_m]Rupert[/name_m]! They fit style wise and flow really nicely together.
[name_m]Linus[/name_m] is my favorite with your older two. That said, [name_u]Benjamin[/name_u] [name_m]Linus[/name_m] was the name of the main antagonist on the TV show Lost some years back and that was my immediate thought when paired with the middle [name_u]Benjamin[/name_u]. For what that is worth 
Good luck!