Invited to celebrate my twin sisters birthday

If you are going away for the weekend why does it matter where your in-laws live, they can surely "go away" too for that weekend? If I was your in-law and found out that you, my DiL, were having a joint party - whether home or away - with your twin sister, and that she was inviting her in-laws, I would feel incredibly upset that I wasn't invited too.

I don't think that you should decide for your in-laws about whether they want to go away that weekend or not - they can always say "no thank you" if there are any particular difficulties in them getting away. Maybe your overall pattern of behaviour can throw a light on to why these difficulties with your DSis and friends are happening?

Tonight a joint friend said we would have to have a drink at a later date since we were going away for my twin sister's birthday. Im super irritated by this.

What did you reply? As a twin myself I would have had to say something.

It sounds like your sister has arranged her own party, and has invited everyone "please come to my birthday". It's confusing why you think it is your party too, just because you're sisters. It would have been nice for her to be noble and include you, but after 40 years maybe she fancied one party that was just for her, and that should be ok. The problem is that you have just assumed she MUST share, is that because your parents always enforced that when you were little? It would be good to ask her if it could please be a joint party and take on a fair share of the arrangements, but you'll have to be prepared to be gracious if she says no.

If I were you and the situation is I understand it, I would politely excuse myself from the upcoming weekend celebrations at this point and work on making some new friends of my own. No need to fall out with your joint friends but this all seems a bit silly and complicated to me!
I have a very strained relationship with one of my siblings and distancing myself from him has been the way forward for me.

I'm guessing your sister organised it and sent invites?

Yes, we need clarity on this.

Are they expecting you to have a separate birthday celebration? That's the only reason I can think of.

Why, just out of interest, do you have the same set of friends? Do you (both) have non joint friends?

Are they not just joking?

Unless you are co-hosting and organising then I think they are right.If you just happen to be there but your sister has done all the invites etc then you are just siblings that happen to share a birthday.

I'm assuming tangible invites weren't sent out but a text and if that said "Hi guys, I'd love you to celebrate my 40th with me, I've hired out X house for a weekend a way." Then it's her party you happen to be going to, if it was something like "Hi guys Megssy and I would love you to join us at X house to celebrate our 40th" where it's explicitly your celebration too then they are being very weird.

Just because you're twins doesn't mean everything has to be joint.

Did she agree to a joint party?

Did your twin sister organise the whole thing? That might be why.

Were the invites from her or both of you?

There’s been another thread like this, I can’t remember the outcome but there might be some useful suggestions on there (although I’m rubbish at searching so will be no help finding it).

Is she hosting or are you both hosting? If it's the former then it is her party.

Obviously your sister has made it clear that this is HER party. My younger brother was born on the same day as I, he still has his party (I don't like to celebrate my birthday). So if you want a party go ahead and organise it. You're not 7 years old so your sister can organise a party for herself and you should not insist on it being your party (everyone knows it's your birthday as well) or people will think you're childish and immature.

Are you putting equal effort into organising the event?
It sounds like your sister is organising her 40th birthday and you have been invited. You need to clarify if it is a joint celebration to avoid any confusion on the day.

Who’s organising this ‘joint’ celebration? Are non joint friends invited?

For back ground we have a strained relationship but despite this have a very close (or so I thought) set of friends and always kept are issues separate.

I’m thinking your issues might not have been as separate as you thought they were.

The frosty relationship between you and your sister has definitely impacted the dynamics of your friendship group and if attendees are referring to the birthday party as just your sister’s party, then you know exactly where their allegiances lie.

Well, if you get there, have dinner and everyone sings “Happy birthday, dear Sis” then moves on to the rest of the evening, won’t you feel like a chump.

I think you need a very dispassionate look at how this celebration will go before committing because I don’t see the word “share” in your post coming from your sisters end. You could be setting yourself up for a world of hurt.

Then the invite must have been for your sister not both of you?

I'd tell people you know it's a joint celebration right?

Bring it up make sure people know it's for both of you. Tell those who are going.

Is there cake? Are you involved in planning?

My sister and I have the same birthday (though are not twins). This year she had a party on our birthday to which I and our family and friends were invited. It was very definitely her party not mine as she organised it. Have you organised this one? If so then I think it's odd it's not your party too.

Clearly, she’s arranged the party and invited people
to celebrate ‘her’ birthday. Your problem should be with your sister not your friends. Maybe she’s done all the organising and is fed up of you just expecting to share all the benefits (you say you’re not that close, I’m presuming there is a backstory).

I think your own sister sees you as an invitee that happens to also have a birthday the same day rather than one of the hosts.

”What are you talking about! It’s a JOINT party for twins. Did you even read the invite? 🤣”

"I said not to invite mine"
Sounds as though you aren't the one organising the party and inviting people, so not really your party.

This is super weird and maybe reconsider inviting your in laws? Can you ask your friends outright why they keep on referring to it as such. I would wonder if it is your sister, who had planted this seed and said oh it’s my birthday, I’m organising it and I’ve invited Megssy.

Well it all hinges on who did the inviting and what the invitations said surely? Presumably they made it seem like she was organising/hosting an event for her birthday? Otherwise all your friends and family are being weird in the same way at the same time which doesn’t make sense.

That's weird. YANBU