Children's party invite etiquette - what would you do?

[QuercusQuercus]

It's my daughter's 3rd birthday soon. We're having a little party. She's at the age now where she's formed a few special connections with other children at her nursery and in our friendship group, and we'd like to invite those children to her party.

At nursery she is particularly fond of one little girl. My daughter's key worker reports they play together, I've seen them run and hug when they arrive for the day, and when we're at home DD will mention this little girl as her friend.

The little girl is one of a pair of twins, and her brother is also at nursery. He is not friendly with DD - in fact, she quite often says he hit her or pushed her, that her key worker had to tell him 'gentle hands', etc.

I'm aware they're toddlers and they have their skirmishes, so this isn't a major issue day to day. However, I'm torn as to what to do about party invites. If the little boy was unrelated to DD's friend, we wouldn't invite him, as he isn't one of her buddies and we're probably only inviting 2 or 3 kids from her room. But as he is her twin, I worry I'll give the impression he's 'excluded'. Is it OK to invite one twin and not the other, or is that mean?

If any of you more seasoned party throwers could advise me, that would be great.

When dd was younger we would invite both children even to an all girl party - occasionally invited another boy too because I was friends with his mum to add the number of boys (I did this twice only)
However, my dd got on well with both boy and girl in the twin pairing.
If she didn't get on with one or the other, the disliked one would not have been invited.
Now dd is older and even though she gets on fairly well with the brother, we have only invited the sister.

@rocketgirl22 DD has many boy friends, as almost everyone in our NCT group had boys and these are the children she's hung out with and got to know and is excited about being there. So girls only isn't really an option. There'd be about 3 kids there

I'm still leaning towards inviting DD's friend and mentioning that her brother is welcome too. It seems the best compromise, from the responses here. It means I'm not second guessing the parents' preferences, and they can decide what's best for them and their kids.

Sod's law says that after all this, they won't be available

Just a thought... if he is being a tad aggressive towards your child maybe he is a little jealous of her relationship with his twin? Excluding him further may not help that situation.

Someone suggested invite the girl advising son can come too if its an issue ... I think thats the best idea :)

Of course it's fine to invite one twin and not the other, just like it's fine to invite one sibling and not the other!

I don't have twins but a 4 and almost 3 year old. Last weekend 4 year old went to a party, this weekend it's 3 year old at a party. They might not like it, and it means husband and I divy up child care, but such is life.

Do you know the twins mum or dad to chat to? I had this dilemma at nursery age. I chatted to the mum about it, she was very keen that her daughter's be seen as separate people rather than just "the twins" so she was more than happy for us to invite one and not the other.