is this a bit rude? Or just me?

Yes sullen and joyless with one word answers. This is OPs home and they are guests.
Hello OP, How are you?
and No thanks , I’m heading off home shortly.
would have been a more social response.

I read all the gentle parenting books and followed those groups for a while when mine were smaller, and they recommend not telling your child to say please and thank you, because you’re forcing them to say it when they don’t mean it/understand it (when they’re very little), and instead that you model it, so you say it yourself or for them when they’re small (in the hope they start doing it themselves in their own time).

I honestly think this is doing children a disservice, because they then don’t get it ingrained into them as something you just say automatically- which means that when not with their adoring parents, but other adults in their lives, they come across as rude.

Even my three year old says ‘thanks’ when given something - does she truly mean it/understand it- probably not, but it makes people in shops/cafes/pre-school warm to her, and will affect how she’s viewed and treated as she gets older and I’m not always with her. I’d be mortified if she didn’t say thanks in that situation as a 19 year old.

(To add, I am not against gentle parenting in general, if done properly and not just as an excuse for permissive parenting. But this is one element I think she’s mistaken on. I’m all for raising independent thinkers and not people pleasers - but saying please and thank you and generally being polite doesn’t make you a people pleaser, it’s equipping your child with the essential skills of interacting with whoever they meet, and it’s not fair to not properly teach your child this).

What invite? She didn't invite them for tea?

She asked if they were stopping for tea, which they weren't, so they said no. Seems perfectly acceptable to me.

Although... I've just realised, it does probably depend on where you put the emphasis in the sentence.

As I never make tea for my 19 year old, it would just be a simple question in my house, meaning exactly that - are you stopping for tea? A simple no would do in reply.

However, if you are the person who actually makes the tea in your house, it then becomes an invitation, requiring a no thank you.

Do that make sense? Or is it just me?!

We don’t know that she would be making it, if they said yes she could have turned to her daughter a d said she needed to sort it / order a take away etc

i think there first response was appropriate. You asked if they were staying for tea - this doesn’t sound like an invitation, an invitation would be more would you like some tea. Saying no thank you only makes sense if they were being offered son - whilst you were it didn’t sound like it so in their mind wasn’t.

Or maybe that came across as hollow as they had already answered that they weren’t staying. Yes, they could have said thanks to that, or they could have thought the previous question was “don’t you think it’s time you left as we’re eating soon” in disguise.

I must be losing it. If someone said to me, 'Is anyone staying for tea?', if there were more than one of us obviously, I would respond with 'No I can't Imsoshocked sorry, but thank you', or 'Yes that would be lovely thanks...but can you meet my dietary requirements?'

They were rude, 'thank you for the invite but no thank you' would have worked!

And then this happened, according to the OP

I said, "ok, well you're both very welcome to stay in you'd like to." Which was met with silence.

So bollocks to that. They were indeed rude.

I cannot believe the excuses people making in here for these teenagers

They should have said 'No thank you, Mrs..X., I am not stopping for dinner, but thanks for the invite'.

It’s rude, and this is my experience of teenagers.

Yes, super rude. I have a 20 year old and I'd be embarrassed if she spoke to anyone that way.

I agree with this. If the question had been “would you like to stay for tea?” a “thank you” would be expected in the answer, but “are you staying for tea?” I think is fine to answer just “no”, as it’s not really an invitation, more like someone asking if they are going to have to cater for two more people or not.

PMSL at the excuses being made for these ill-mannered brats.

What? The OP said 'Is anyone staying for tea?'. Why does she have to explicitly say first that she is going to make tea? If she's asking if anyone would like tea, surely it's a given that she's going to be making it.

This is the only reasonable comment to excuse rudeness IMO. They could've just been discussing something really emotional for them as a group.

I can't believe people are questioning you on the way you phrased the invite/question OP. Some of the comments made me laugh a little.

I don't think you are being unreasonable at all to think they are rude, unless what quoted poster said.

You asked a question and they answered it. I have worked with young adults, and adults who would hear that as a general question, no as an invitation/offer to stay for tea. If you had said" I'm going to make dinner, would anyone like to stay for tea? " then I would expect them to say no, thank you/ yes please. So, no, I don't think they meant to be rude.

Is this on the wrong thread? Can't see how it was necessary

I think actually the word for this is "sullen". It's not rude per se, but completely joyless and leaves one feeling rather flat

Exactly... the correct answer would be "Oh are you sure? that would be lovely!" or "Oh no we're just going, but thanks anyway!"
said with a cheery smile and eye contact.
When my friends used to come round (late 80s), even if my mother made them just a sandwich, you'd have thought it was a cordon bleu meal. Lots of "That was delicious, thank you...oh are you sure you don't want help washing up? "Not in an obsequious way, but friendly and I suppose appreciative!

They were rude, especially given their age. It might have been that you interrupted an important conversation where they were disagreeing with each other about something but given the behaviour of her friend it's likely that they are just rude.

I would've just said oh okay then that's great, I'm going to have a dominoes and a bottle of wine. See how they like that!

Yeah that's not the same at all.

I’m being genuine.

DS2 ‘s and DD’s friends have impeccable manners.

DS1’s friends are socially awkward uber-geeks. They are well meaning but frequently miss social cues and reply bluntly to what they think the question is. A lovely pair of lads at heart, but often come across as brusque.

As a result, my bar for what is rude is based on intent more than phrasing. As they could easily have heard “are you eating here” as the same sort of question as “are you leaving at 4,” an answer of No is fine.

Had OP asked “would you both like to stay for dinner tonight” I agree a flat No would be rude.