"Graphista, I’m wondering how many people will read your post and know their granny and yours were peas in a pod" I used to think all grannies were like this, as I got older I learned it seems to be a culture/class thing. Mainly true of scots Irish grannies or if not then those from a poor background.
"For thr next 15 years until she passed, the woman had the same pot of mince on the stove, and was always trying to get you to eat it." Unfortunately this also rings slightly true - it took a fire for my mother to be told you need to clean the grill pan and chip pan apparently! She was so fastidious with all other cleaning I was shocked to learn she'd never cleaned the grill pan or chip pan unless we were moving! This was approx every 3-5 YEARS! 
DuggeesWoggle (some brilliant usernames on here mines boring) are your lot farmers by heritage? I've noticed they also tend to be "feeders".
MidniteScribbler I'm struggling to think of a part of the world where the culture generally ISN'T to welcome guests with provision of food and drinks. I've relatives that have travelled extensively inc parts of Africa and Asia that are extremely poor (went as part of charity/gap year programmes) where people give their own food for the week to visitors! Where on earth are you talking of? Exact preferred options perhaps not but certainly would attempt to provide things they recognise and are acceptable to THEIR culture.
I've relatives and friends living all over the world and I've lived outside the uk myself and I've loved learning the different traditions, trying different foods and drink (and if I could order certain foods and drinks to be delivered to uk from certain non uk supermarkets I definitely would there's loads I miss from Netherlands, Germany, Belgium etc) but providing sufficient to guests is generally speaking a worldwide etiquette. Plus I don't think basics like bread, cheese, fruit are exactly "fancy" nor is cornflakes or weetabix (generic versions are available) instead of muesli - which itself is not only fancy but rarely to the taste of children, many adults don't like it.
DoinItForTheKids - cheese on toast MUST be made with strong scottish cheddar on thick sliced white, and yes plenty of molten cheese that you have to wait a few mins for it to cool down a little sweet pickle to cool it down is nice too.
GreatDuck - my mother is generous but her plates are smaller than mine. She's had them over 30 years (and not one chip - how?? Especially with me and siblings using we're not known for our lack of clumsiness!) my side plates (modern sizing) are almost the size of her dinner plates. Plus myself and quite a few others have confirmed with similar experiences of our own so it's not that unusual clearly, but yes you often claim to 'not understand' or think posters are exaggerating. You seem to think only your experience counts. And not just regarding this issue either.
Good for you op. Going forward you and dh might find value in reading up on toxic families and fog (fear obligation & guilt).
Bluntness100 I don't think it's a bit much at all - to not even provide sufficient BASIC food to your DC and grandchildren is appalling behaviour ESPECIALLY when having benefited from their generosity on several occasions AND when the matter has been raised STILL not addressing the issue. Like pps, particularly with the info re when dh a student, I suspect this is a final straw moment. It's why I asked if dh was only child as I suspect he's the scapegoat.
LyingWitchInTheWardrobe thank you
"There's some definite over thinking of the Subway comment going on here from some people" yes I read that as a lighthearted comment from dh :
Smiling dh "ok ok - I promise we'll get your favourite thing on way home"
Subways can be huge too - foot long? I've never had one would never manage it, but dd has been known to chomp through one after a swim. Plus there's tons of fillings (I love the veggie pattie, which I have 'toasted with cheese' with loads of salad inc olives but no onion and thousand island dressing )
MingeUterus excellent post re 'obesity argument'
I use my own toiletries due to allergies but I well remember visiting 'home' (dad was army - several weeks of 'holidays' for us were actually staying at grannies or aunties houses) and certainly my parents used the toiletries available at whoever's house we were visiting (and sometimes discovering new beloved products) and when they visited us vice versa. The only time this didn't happen was people were told not to use my stuff (hard to get, some prescribed due to the allergies) and same for my cousins stuff (same allergies different products used). But yea, I absolutely can't imagine my grannies or aunties being bothered by my mum - their dd/DIL/dsis/sil - using their shampoo!
As for the lack of soap/handwash and hand towels - as an OCD sufferer that would have had me scarpering! Would not want to stay in a house where they clearly don't wash their hands after using the toilet!!
Re "what's cut and come back cake" traditionally a fruit cake but generally my understanding is any very moist cake that is fairly robust and keeps well without drying out - hence you can cut a few slices from it, leave it a day or even 2 and its still moist and tasty when you "come again". The joke with my grannies making such cakes though is they were lucky if a cake lasted 6 hours! As good bakers with big families their cakes were soon devoured! One granny got dementia and had carers coming in for a few tasks - they were coming in purportedly to care for her and she was sending them away with their dinner inc pudding! One of the issues we had with her is she'd get up in the middle of the night and head straight to the kitchen and start baking! At one point there was nigh on a gross of scones to get rid of!
MyImaginaryCatHasFleas - given the age of the DC I'd be surprised if the in laws were much older than me or may of those posting on thread! I'm 46, potentially old enough to have gc not that much younger, my parents in their 70's were alive during rationing but too young to remember it and my grandparents who would have remembered would be well into their 90's if alive - I think it highly unlikely that's the issue. More likely they're the age of some of my younger (parents both eldest of big catholic families) aunts and uncles. Who certainly don't remember rationing and cater generously for family gatherings.
From various comments it sounds like this isn't even how the in-laws eat when the op & family aren't there.
If the in laws regularly ate like this they would not be 'not thin' AND they wouldn't be capable of eating much more when it's at op's & dh's expense, AND wouldn't be sneak eating extras! My parents used to do the cruise thing too - I rather suspect these in-laws are the type they described as not only gorging at the buffets but hoarding food away in their cabins and 'sticking up' by secreting away food in luggage at the end! U agree with MingeUterus - it's the combination of info that's lead us and op to our conclusions of tightness.
Where I live (ironically Scotland) it is indeed very sparse as far as shopping goes. We've one supermarket, couple of convenience stores. Not that far from me there's the islands where the people don't even have that, they come over by ferry in 4x4's once a month to go to our supermarket (ferry alone is about 50 mins and then I think maybe 20 mins to supermarket?) and the other shops too (which are also rapidly disappearing) and they think of this small town as almost cosmopolitan in comparison! I've friends in the highlands who's nearest supermarket is over an hour away and not that big even. They've one small convenience store in the village. There are certainly parts of Wales and England like this too - I've either lived there myself or have friends who have (army bases tend not to be in city centres).
"He could easily have bought extra cheese, meat, yogurt, jam, cereal, biscuits" the kind of small convenience stores in very rural places rarely have large stocks of perishable goods, my local convenience place certainly doesn't sell meat, and the other perishables are usually sold out by mid morning even at weekends - these type of shops tend to know their market pretty well and only get enough in of perishables to meet their usual sales, perhaps a little more. Definitely little variety and usually heavily marked up top brands.
I'mNotasgreenas - food issues aside I come from a deeply dysfunctional family where stilted conversations, poor behaviour in other ways are definitely a thing. For those posters LUCKY enough not to come from such families OF COURSE it seems odd, and it isn't the norm for most but for a significant minority of us it's OUR norm (unfortunately). My ex found it extremely unsettling, he being from a relatively 'normal' family (all families have their quirks and peculiar ways of doing things - eg Christmas dinner has been mentioned on this thread, I've only been on mn a couple xmases, but I've noticed how heated it can get over relatively minor differences in how family's 'do' Xmas - what does Santa provide? Stockings only or big gifts too? When are presents opened? When is dinner served? Do you watch the queens speech? Go to church? - then of course when 2 adults who's family's did Xmas very differently get together who are BOTH sure THEIR family's way of doing Xmas is 'right' you get all sorts coming out!! My ex and I our first big argument was over Xmas plans. For me Xmas did not have happy memories - alcoholic father who ruined most of them, whereas my ex LOVED Xmas) as MummyofLittleDragon says it takes little in such families to damn near start wwiii those of us in them and especially scapegoats tend to have LEARNED it's better to keep head down and trap shut!
Why are people finding it so hard to believe that there ARE people who are tight fisted cf's? Certainly plenty of threads on here about them!
Kool4Katz "I don't think they had many friends" 😂 no I can't see that attitude and behaviour going down well AT ALL in the highlands!
"Mean with money, mean with love." Just what I was thinking.
Runbeer:
If any of the mum's in my family served those portions I would not be at all surprised to hear (particularly from the male members who all do manual/active jobs) "ok that was the appetiser what's for starters?" Or actually more likely "I'm not a bloody rabbit where's the real food?" (Usual comment for whenever salad served). I'm veggie - both grannies interpreted that as "must give Graphista double portions" I'm 5' 2" and was a size 6 at the time! Hardly a big eater!
From your latest update op I was initially sceptical of pps saying maybe they were deliberately trying to get across that you weren't welcome...now I'm not so sure. Utterly bizarre cold behaviour! Now I'm wondering if dh an only child and perhaps also unplanned? I would not be surprised if you were to discover these were people who never really wanted DC.