To think this isn't nice?

[KungFuCheetah]

To not go and visit a sibling and their partners new flat as soon as they move in as you say you are finding it difficult not having your own place yet?
They said they will go to visit in a few weeks or so..

Do you mean that your partner is annoyed with your sister because your sister hasn't been to visit yet?
TBH your posts aren't terribly clear.

He feels it is unsupportive and childish especially at her age

How old is she then?

Thirties ,and yes that's what I mean @TheShellBeach

Partner needs to get a grip!!

This is now causing tension as the partner of the sister is very annoyed and upset that she will not visit. He feels it is unsupportive and childish especially at her age

So, in summary-your wealthy boyfriend (and you) are pissed off that your sister hasn’t visited your new flat as soon as you move in because you really need her support?

Why exactly do you need her support? In what form do you think support from your sister will help you? With the unpacking?

Why exactly do you need her support? In what form do you think support from your sister will help you? With the unpacking?

I was wondering the same thing.
OP why do you think your sister should come and support you? What do you need help with?

And what has your sister's age got to do with the price of fish?

It's a bit pathetic not to show joy for your sibling having achieved any big life event (baby, new home, marriage, graduation, new job, whatever).

Mate it's just a house. Get over it. No one else cares. You don't need support.

Think it's because the OP wants to crow 'look at meeee with my wealthy boyfriend! Come pay fealty and let me see your envy, I am younger than you, nnnener nnnener nnnener'?

Can you please write your posts clearer?

I think you are saying :

you and partner just moved into a new flat. You are disappointed that your sister/brother won’t visit right away. They will visit in a few weeks when you’re less excited. Your partner is weirdly over invested in all of this and is also annoyed.

If that’s correct, then yes I can understand your disappointment. But it’s a good lesson in people (even family) have their own lives. Don’t let their reactions affect your enjoyment. Your partner’s reaction is odd and he should probably stay out of it. Your sibling’s reasoning, if they specifically told you the reason for not visiting is also a little weird but probably explained through a series of sibling rivalry events you had growing up.

Edited to fix a lot of typos… cat sitting on lap