Are our friends being cheeky?

This. @luckylavender you'd end a friendship if they didn't do what you want, in their own home?

I think it’s really hard to say no here actually. I’d suck it up, and think of something that’s easier to have just the 4 of you next time- a show?

This is good bc it outlines you’re not massively keen and puts them back on the spot of directly asking - it will show whether they’re thick-skinned and determined or sensitive to her not being welcome I guess

Maybe, it just feels like the approach that British sit-com characters take to avoid conflict and end up getting themselves in deeper, fibbing and hoping for the best instead of saying what they mean.

They've asked a question that has yes or no answers. OP should be able to say no, and if that ends the friendship because it was a trick question that had to be answer yes or else, then it's not on the OP. However I think this friend knows that it's not a given DD has to come so I think they'll be reasonable about it.

I find it a pain when an adult child attends a much anticipated meet up - it really does change the dynamic as you end up asking lots of questions about their studies/ job etc rather than having a good old chat and a laugh.

But hopefully the daughter won't be visiting on the rearranged date

Your friends are being cheeky and they have put you in an awkward situation.

I agree with others suggesting there may be something going on in the daughter's life to suddenly want to spend seemingly every weekend with her parents but as friends, obviously you want to spend some time just as the smaller group.

I would reply that you would prefer not to include the daughter on this occasion as you were looking forward to the dynamic between just the 5 friends but if that's a problem this weekend would they rather change the date?

I think it also depends slightly on the ages of the people, i.e. if you and DH are in your 50s, your friends are in their 70s, the mutual friend is in their 40s then the unreasonableness (or otherwise) if different than if everyone, bar the DD, is in their 70s.

Nonetheless, I think I'd probably suck it up on this occasion, but consider how/if you want to see these friends moving forwards if they now come as a 'thruple'

The DD HASN'T been invited by the people's whose home it is! Only her parents who have rudely decided they get to do this!

It's not univiting the DD, she was never invited in the first place
If I was OP I'd be messaging the friends and saying to not worry about coming if they're busy hosting DD and asking them to let me know when they're free to catch up
It changes the dynamic of the group, she's been polite when she's been over to their house and it was their decision to have their DD. OP has no reason to adopt this grown DD in to the group. Whether DD is having a bad time or not is irrelevant, OP is not responsible for them, she is not friends with them and if she accepts this once, it's likely to end up a regular thing that it is assumed the DD is welcome to tag along to everything

I'm as direct as they come but I don't see how you can say no and maintain the friendship.

To me it feels a bit odd that you're so anti the daughter. Unless she's absolutely awful, I'd have felt I'd probably made friends with her from meeting her at theirs. So I'd be happy to have her along.
If she was a child or teen I'd say it would be more awkward. But as an adult surely you can talk freely and include her in the conversation?

But if you don't want to then just politely decline. It's true to say they shouldn't be pushing her on you!

I agree; my first response would to be to ask if everything’s alright with her as she didn’t used to come to the meals but now does. Alternatively, maybe she just really likes your company…if her parents had her young she may not feel the generational difference and may think she’s one of the gang. How much younger than you is she?

If you did the cancelling/excuse option for this meal, I don't see why they'd take any kind of hint that the DD was a factor so it would need spelling out, hence better to say so now when she's asking if DD can come. They shouldn't be offended by a response like the one a PP suggested, rearranging for when DD isn't there, and if they are, well, they're the ones creating the situation not OP. Anyhow, the meal is this week so not much time to agree then cancel with a viable excuse and lying about such stuff doesn't come easy to everyone.

Why is the daughter suddenly featuring in their social life? Has she had some upheaval in her life, is she lonely or depressed? It is unusual for a 40 year old to be socialing with her parents friends.. If they are trying to help her out in some way, it would be unkind of you to try to exclude her.

Yes it messes them around but frankly, that's their own fault, and it's done with the intention of avoiding offence. I'd hope not to need to actually spell it out that the daughter isn't invited.

I don’t see how you can uninvite DD; she clearly wants to be there. Maybe she’s not got much of a social life and gets more out of spending time with you than vice versa. I’d probably roll with it, for everyone’s sake.

That's so much more complicated and stressful and messes people about more. And if you're ultimately going to have to be clear that invites are just for them, might as well do that out of the gate now.

Rather than offend them, I would agree and then make an excuse to cancel a few days before. I'd then rearrange for another time and hope to god they don't ask again about bringing the daughter. If they do then I'd make it clear the invitation was just for them.

Some posters are forgetting you said you and your DH aren't very social, if you prefer only to see closer friends that's your right especially in your own home.
I'm always saying on here to start as you mean to go on, if you're not comfortable now with the DD coming it's better to say no, if her DPs want to make it every time it's much harder to backtrack

I think this is a good response. Trouble is, OP is inviting them round to dinner at their house, not a meal out, so it'd have to be something like:

"Hi X, no worries, totally understand you want to spend time with DD so let's reschedule a meal out for all of us on X date instead. I'll be in touch with some dates."

Unfortunately this sounds a bit more pass/agg and complicated!

I would say we were really looking forward to an evening just with you both and X, so we’d prefer to keep it that way this time. That way it is clear that you are not open to discussing it, apologising etc.
Has the daughter just suddenly started to be there more? She may well be going through something and her parents are trying to support her - which is great but doesn't mean they start asking fr her t be included in every where they Go

That's fine if you're a 'come one come all' host who likes chatting to everyone, but some people like chatting to specific friends about specific things and it's just not the same when there's someone else in the mix who you're not close to. As a one off, it might be novel/interesting to include a friend's relative, but beyond that, there's a reason we're friends with our friends so it's them we want to see. Plus it's them as our friends, not them in parent mode, which even with a DD in their 40s will be a different persona. Groups have dynamics and can be hard work with others in the mix instead of the pleasurable things they're meant to be.

They obviously think you like spending time with their daughter as much as they do. You have to say no, just try one of the ways posters have said on this thread. They probably won’t like it though, just remember they changed the dynamic of the friendship first not you.