I’m told names are too short

Agree with PP, it's the type of name and the gravitas that doesn't match Penelope.

Penelope is a beautiful classy classic name.

Evie, Elsie and Hallie are twee chav names, sorry to be blunt. They're incredibly common in all senses. They're also nicknames which doesn't give the freedom of a longer/full name like Penelope. I would feel sorry for your second daughter with one of those names.

Never tell people the name(s) before birth! Except here, obviously.

Penelope & Evie is like Sebastian & Dave.

It's not the length of the names that don't make them go with Penelope, it's the gravitas of them.

My name is a short, one syllable name, and my surname was also one syllable. I hated it - there was no rhythm to the name - eg Ann Lee. My sister, in the other hand, had a long and pretty four syllable name, eg Alexandra, and I always felt hard done by and as though my parents had chosen a really popular but boring name for me, and an unusual, beautiful name for her. I know in reality they struggled with her name and she was 3 weeks old before she had one (she's a lot younger than me so I remember) but still I wish I had been given the same consideration.

I'm sort of with your family on this, although you have gone for two syllable names at least.

I agree that telling rellies in advance opens you up to unsolicited advice and best avoided, but actually I think they're right about the subject at hand.

You need a name that makes the DCs look as if they are members of the same family.

Suggestions:
Susannah
Cecelia
Alexandra
Beatrix
Elspeth
Katherine
Annabel
Theodora
Emmaline
Madeleine
Flora
Charlotte

They do have a very different vibe but that's not really anyone elses business.

Penelope is nice. It's different, but not unheard of or overly modern sounding. It has nickname options (presume you call her Penny?). The ones on your list are extremely overused and bland sounding. They must aren't the same style.

You obviously like very feminine names. How about:
Felicity
Meredith
Elspeth
Miriam
Josephine
Romilly
Matilda
Rosanna
Tabitha
Elizabeth

@BertieBotts Eve isn't really a fad but Evie certainly is!

OP your children's names are your business (and the other parents) but no one else's really.

The names you've suggested don't really 'go' with Penelope in terms of style and they all end in "ee" sounds but if you and your partner love them, that's your choice. The won't be introduced as Penelope and X their whole lives.

Does Penelope get shortened to Penny for everyday use? Penny goes well with all three of the names you've chosen (which are all nice names btw).
It might be nice to pick a longer name for the BC though, so she doesn't possibly feel hard done by later on in life, in comparison to her sister! It also gives her more options should she choose.

I once worked with a lovely girl called Halina which could work for Hallie if you weren't keen on Harriet.
Eve / Evelyn / Evangeline are all lovely, and Elizabeth for Elsie.

I really love Elsie

How about Jemima or Clementine or Verity if you want a longer name. I'd stick with Elsie though.

Congratulations

You can't go wrong with any of those names my fav is Elsie but they all work fine

I LOVE the name Hallie.

My name is short (one syllable) and I have no middle name. I'd much rather that than some of the mouthfulls you read on here!

Eloise instead of Elsie? ‘Fits’ with Penelope

Penelope is beautiful and classy.

Evie is overused and trendy, so it has a very different feel. Elsie is also quite trendy, whereas Hallie stands out and feels more like Penelope.

So it's not about the length imo.

Tell them that on reflection you agree with them and are therefore naming her Persephone

I think Evelyn or Evangeline, in Evie would go nicely with Penelope. Eve is nice too though - both classic names with history.

Generally speaking I would only worry about names not going together if there is a clear established theme to other sibling names, or a very obvious clash. E.g. if you had Penelope, Josephine, Alexandria, Evangeline and Ruth then Ruth would stand out as a different style of name. Same if all names bar one were from one culture, for example in my family there is a group of siblings all of whom have very Welsh names except for one - think Llŷr, Siôr, Angharad, Esyllt and Malcolm. Malcolm stands out and got comments about his paternity growing up as he didn't match his siblings.

I don't think you're in that territory with your choices.

Penelope is a tad unusual, Evie and Elsie are very common. I think that is more of an issue for me than name length.

Penelope and Evelyn/Eveline/Elspeth do 'go' better to my mind, if that's something that's important to you.

How on Earth is Eve/Evie faddy? It's biblical FFS. One of the oldest names there is.

I’m not particularly keen on your choices of name for your new baby, but it’s neither my business, nor that of any of your family members. Choose a name that you love, or you’ll always regret it. That’s far more important than choosing something that “goes” - a concept I don’t understand either.

Why do family even know what your list is?! Keep it between you and DH and choose the name you like

Some people care if names 'go' and some don't. I personally do care. I wouldn't have a Charlotte and an Indie for example, despite liking both names, it just feels odd somehow and naming is important to me, I'd want to get it just right.
If I met a Penelope and an Evie/Elsie sib set I would probably think 'oh that's unexpected' for all of 5 seconds and move on, not a huge deal or anything but as OP asked...

Love all those names!
My sisters name is long (similar to penelope) and mine is short (similar to your 3 name suggestions too) I'd never have thought of it as an issue in a million years!
Her name is often shortened to a nickname, mine can't be shortened, doesn't both me at all, I actually prefer my name

why do names have to go together? (But yes - Evie is the new Emily/Charlotte/Shannon)

Honestly? I agree with them. But it's your choice in the end. Penelope is long, lots of nickname options and has substance and won't date her to any particular era.
Evie/Elsie/Hallie sound like nicknames and are quite faddy. So many girls are called Evie these that one day it will probably be the new Sue or Linda (No offence to those names, I know some lovely Sue's and Linda's)
Although names don't have to 'go' I think I would be envious of the name Penelope if I was called Evie.

Evelyn would go really well.

I don’t think names need to ‘go together’, I’ve never heard of it anywhere other than on MN.
And lesson learned, never tell anyone the names you are considering, just the name you have given baby when it’s born.