Your kids have lovely names! 

I love Eloise and think it goes well with the other kids and your surname.  I think it's a great match to "klara" as a sister. Vivienne is also lovely, although I think I just slight prefer Eloise. Vivienne would be  a close second though. Dorothy I just don't overly care for. It sounds a bit frumpy to me. I know others love it though.

I love Iris, Esther, Aurelia, Colette and Mathilde with the your current kids.  Colette would be a lovely choice if you wanted to stick with the C theme without being too matchy in sound. I think they make a nice group.  Aurelia seems well matched to the 'prettines' of Klara. I do find it has pronunciation variations but that might not bother you. It is a lovely and under used name. Iris, brings out the old-lady vibe of the names (I mean that in a good way). Maybe if you associate it with eyeball though it isn't the best choice? Mathilde is an absolute favourite of mine, so I would probably say this is my favourite. Esther I like, but again it can have pronunciation variations, it is chic-old lady to me.  All of these seem like good choices, go with the other names, and work with your surname. I also think they all work with Mae as a middle name.

Briar is a long time favourite of mine but I find Briar and "Klara" too matchy in sound. Everly seems to be a departure in style.

Other suggestions: Clementine, Alice, Lucia, Allegra, Susannah, Rose, Genevieve, Nell, Elinor, Harriet, Hazel.

I love your childre's names!  I like the idea of another C name, especially if this is likely to be your last child. Colette is nice and I also thought of Cassandra, Claudia and Cordelia.

For non-C names, I really like Mathilde and Esther for you.  I adore the name Iris, but if you think of eyeball maybe it wouldn't be the best choice!  For the sound of Iris, maybe Isla?  I also though of Viola.

I happen to kind of like Alma.  Amalia has some of the same sounds and I think it could work as a tribute to Alma, maybe you'd like it better?  It also gives you the nickname Molly which would be adorable with Klara.

Of your top 3 names, Vivienne seems more...exotic and romantic? than Konrad and Klara.  Eloise is not a name I am usually a big fan of, but I think it works very well with the sibling names.  I also like Dorothy for you, though slightly less than Eloise.

Some other names for you to consider-Agatha, Ophelia, Delia, Beatrix, Eliza, Helen and Pearl.

I adore Eloise with your other children's names.

My only hesitancy is that it seems poised to become the next big thing, but perhaps that's my imagination, and perhaps it's not a concern for you.

I do like Dorothy. It is a bit frumpy and middle aged, but I adore that sort of thing on a little girl. I think you could also come up with a more modern nn if you wanted-Thea, Dorie...I do prefer Eloise overall, but I think it's a fine option.

I'm not personally a fan ov Vivienne, though I know others are. I also find it a bit fussy with your other children's names.

Klara and Konrad (with Cs) are a fine, sturdy pair in my imagination. Fair haired, rosy cheecked, striding up the mountain side...

To that end, I think Briar, Aurelia, Everly, and Colette are all too princess-y and delicate.

Mathilde seems pretty much perfect. It would be very close between it and Eloise for me.

Esther and Iris just seem like the wrong generation to me.

Other thoughts

Anna

Lucia

Ruth

Eve

I also second the suggestions of Clementine and Helen (Helena would be another thought).

Mae would also be worth considering as the fn.

my two faves are Vivien Mae or Colette Mae or even Viviana Mae would sound nice with Klara.

I love Eloise, and think it would go perfectly well with your other two.  Of your top three, Dorothy would be my second choice (although I prefer Dorothea).  Vivienne is fine, but I've just never loved it, and I think it's starting to feel a bit trendy to me as well.  From your full list, I'd vote Mathilde (love! esp. w/ nn Tilly), then Iris or Eloise for a tie (although I think Eloise goes a tad better with your other two), then Esther (sweet, soft, pretty, underused), then Dorothy, then Colette (nice, a little too frenchy and lightweight to me to go with the other two, particularly Konrad, which feels very Germanic to me even if spelled with a C).

Thank you, everyone, for your thoughts!  I really appreciate your reactions and rankings and suggestions.  I think your comments even may have persuaded my husband to like Mathilde a little better!  I do like that it is a German name that fits with the other two.

I think I may have to knock Vivienne off the list - I met TWO little Vivian/Viviennes today at the children's museum - and we were only there for an hour and a half!  Viv is darling, but the local popularity may be a problem (to which I am especially sensitive having been one of so many Jennifers).

I am definately leaning towards Eloise.  Husband favors Dorothy.  I will let you all know in three months!  (And if you come across any other name suggestions, please post them!!)

Thank you!

I very much like the names you've chosen for your son and daughter! Especially Klara, of which I am quite fond!  I like it that you are ahead of the curve with your name choices but that they are personal and meaningful, with the nod to your German ancestry. I would rule out Vivienne for the very reason you did...you can thank Brangelina for that one!  Because of the children's books/movies Matilda is on the rise and I wonder if Eloise is destined for similar name stardom.  Of your choices, Im leaning toward Dorothy.  It's a fave of mine and Dottie is a darling nn.  What about Annalise?  Sounds similar to Eloise, and has the German vibe?

At the risk of getting a little Von Trapp-ish on you, what about Marta or Louisa?  Wait, scratch Marta.  Sounds too much like Klara.