To say this idea is stupid and to tell DH I don't want to entertain it?

It's quite unusual now I think to get a mortgage and never sleep at your parents' houses again, at 18.
My children have gone/will go off at 18 to live, study, and work in different cities. They will come and visit, and spend nights at both my and their dad's house. They are able to do that as they have bedrooms at both houses. I really don't understand what part of that is provoking such a response.

I'm still so confused at the idea that parents are locked into a massive house forever just in case their fully grown adults feel like visiting for a week at Christmas.

This practice is usually (but not always ..... ) confined to people on MN. It's less common IRL

I'm still so confused at the idea that parents are locked into a massive house forever just in case their fully grown adults feel like visiting for a week at Christmas. Surely this is contributing to the massive housing issue we have in this country? Elderly adults blocking young families from accessing decent sized homes in the hope/fear that their grown children might someday want or need a bedroom again?

My mum lives in a 2 bedroom flat with her dog. One bedroom is hers and one is set up as an office. We live overseas and thousands of miles away so if either me or my brother visit her we stay on an air mattress or in a hotel. And somehow we all love each other anyway.

My inlaws live in a massive ridiculous house where they raised their children. They refuse to move and it's crippling them. It's totally unsuitable for their age and is enormously stressful for them to keep it up. We only visit for a week or so every other year so for 99% of the time there are 2 people in 6 bedrooms. Totally ridiculous and quite wasteful as they are obviously heating/cooling it and looking after it. They would be much happier in a condo of some sort.

Are parents just supposed to keep large houses with unused bedrooms indefinitely for the sake of adult dc visiting at Christmas?

I'm aware the step siblings are teenagers so it's not relevant now but at some point like all of us, we need to be made to stand on our own two feet. Should parents be keeping their rooms free for them in their late 20s, 30s just in case?

My own parenrs could very much do with downsizing and moving to a bungalow. It would benefit their health and free up capital for them. But they can't as my useless sibling still lives at home in his 30s and my parents are caught up in the belief that it his home too and he can live there for as long as he wants despite the fact it's holding them back and they are at the point where their health and needs should be prioritised rather than my freeloading sibling who could have moved out years ago.

it's 2 nights a week, of course they can share. You should give your son the space he deserves, the others don't live there all the time so why do they get priority over somebody who does ?
YANBU at all, its just common sense.

Isn’t it a bit shit that it is always the mum expected to house the adult DC not the dad (where parents are separated)

@FlyMeSomewhere have you never stayed with family when visiting, over Christmas etc

I think you are being unhealthy with your kids, you want them to stay by your side and keep you the centre of their world despite being adults!
I had a mortgage at 18 and never slept a night under my parents roof again.

Adults need their own space especially once they get a partner! It's not healthy for grown adults to be still taking part in shared custody rituals instead of having lives of their own! No parent needs to keep a suite of bedrooms for full grown adults! Where do you draw the line! If you have 5 kids and they have 10 kids between them, will you go and buy a 16 bed house for something that just won't happen? Set your kids free instead of making them feel that you need them to stay with you to keep you happy!

But why would they no longer want or need a room at their dad's? I appreciate that might be what pans out more often than not, but is that because dads/non primary don't keep a room for them? Plus they may fall out with their mum, a new partner may move in with her etc, lots of reasons why dad should keep space for them. I don't like to think of an 18 yo not feeling they have a home/room they're comfortable in.
I'm divorced and our adult children still stay with each parent

Disagree with this.
The DH needs to be aware that his wife and youngest DC also have needs and feelings and deserve space to exist in their own home. The current optics are not good at all.

I think if I read correctly the way some posters are making out that the 3 year old should be in the parents room indefinitely while the other bedrooms are kept free for the step children, any future partners they have and future children 🙄.

Some of these replies are insane. Telling the parents that their sex life should be restricted to the living room sofa, that rhe 3 year old should keep sharing with their parents while other rooms remain unused 5 nights during the week. Absolutely bonkers. Of course the 3 year old should have their own bedroom in their own house! The other three children are teenagers and may in a few years not even be visiting as much. Having the two DSSs share a room for TWO nights a week is not a great hardship. Plenty of children do it up and down the country without being psychologically traumatised by it as many on here would have you believe!

She's got a real on at her mums too. She doesn't really need two permanently set up for her to use every now & then.

The 18 will have a bedroom at mums where they already spend 5 nights a week. They seldom want to do 2 night gets at the other parents once they're 18. No need to be so dramatic!

Nonsense

So the OP even if she really desired to have a child of her own, should have been told to forget that dream because the stepkids need 6 bedrooms between the three of them with 4 of those rooms set to be used barely ever by the two near adults and one room used 2 nights a week?

@FlyMeSomewhere yep, the OP should have carried on taking the pill, because step children have far more right to bedrooms that children with together parents!!!

So the OP even if she really desired to have a child of her own, should have been told to forget that dream because the stepkids need 6 bedrooms between the three of them with 4 of those rooms set to be used barely ever by the two near adults and one room used 2 nights a week? You think that should have been a reason to stop OP having her own baby! Jesus! They have ample room if the barely visiting stepkids share!

I'm not sure where I am supposed to have been privileged to not recall any friends having to share bedrooms, it wasn't something I financially benefitted from or that my parents lived in mansions! We lived on new build estates in semi detached houses crammed in like rabbit hutches although not entirely as bad as they are these days, nobody had privileged lives! All of my friends had two working parents and people were happy stopping at two kids back then! You've confused privileged with people living within their means.

Do not fall into the hole of making this a competition between your DS and your DSS in respect of their father. DSS have already had their lives disrupted and they only see their father 2/7. Of course he'll be trying g to make up for that.

Dont make it the issue, you risk derailing AND making yourself the bad guy

@Springtime43 but when they had a child when they were in 3 bedroom house, how would you have allocated children in that scenario?

Surely its a choice to have a child you dont have room for though?! Thats what baffles me. They chose to have another knowing they had no room. And as you said in a further reply, two are almost adults and may not want to stay anymore/go away to uni/get their own place so they could have waited to have another? Then they would have had this issue 🤷🏼‍♀️

But they did have room, it just meant sharing (which has been acceptable for centuries).

And as for bedrooms for adult children, no one is suggesting they are slung out onto the street, just that they don't all need a specifically allocated bedroom in two homes, indefinitely. As long as they can use a spare room, then surely that's fine? Otherwise, six empty bedrooms would be required across two houses ..... whilst a 3yr old has to do without.

This entire situation is ridiculous. The DSC have a place to live at their mum's. Their dad's rooms for them is secondary and of lesser importance. Bedrooms should be allocated by need. I definitely wouldn't be moving to a bigger house and paying half the mortgage and carrying out building works to create an enormous house you simply don't need. It's DH who wants these extra rooms, for his kids.

Right now there's 4 DC and two adults. Adults get the master bedroom, because it's their bloody house! DSS get the next biggest room to share because there's two of them and they're same-sex teens. DSD and DS share the smaller room because although there's two of them and they're opposite sex, one of them is small/young. That's the sensible way of doing it.

The natural progression is that DSD stops coming overnight soon because she's becoming an adult and will be able to visit and go home again, like adults do. That then leaves DS with his own room, the smaller room because there's only one of him. DSS sharing the larger room. Parents in own room.

If you're going ahead anyway with a larger house then honestly I'd say you need to be getting something out of this arrangement. For me that would look like:
Parents having the master bedroom because that's what normal people do and it's ridiculous to buy a huge house and not give yourselves the master bedroom.
DS having the next largest room because he's there all the time and because you, his mother, is paying half the mortgage on this enormous home that you don't need.
DSS have the next biggest room to share because there's two of them.
DSD gets the smallest room because there's only one of her.

When DSD stops staying over, the youngest DSS has her room because he's younger than his brother and you have to allocate the rooms somehow. He can have the bigger room once his brother stops staying over.

Putting DS in the smallest room like some are suggesting, whilst leaving 2 or 3 (depending on the loft extension) other bedrooms empty 5 nights a week like a fucking shrine to the gods of Step-situations, sends a terrible message that DS is less important than people who aren't even there most of the time. No fucking way would I be giving my DC that message growing up under any circumstances (and paying through the nose to do it, too!).

If 'D'H said again about leaving 3yr old DS in with you still, I'd say he's just using you as a cash cow to fund housing for your DSC. He's not even bothered about privacy to have sex, when sex is of huge importance to most men. So where's the relationship then, if you're not able to live as a proper couple just because he has DC from his past marriage? If he insists on you and DS being treated like spare parts in your own home, goes into a sulk or causes a row (or anything other than apologising for being a dick upto now basically), I'd stop the purchase of new house and use my share from the old sale to purchase a two bedroom flat/house where both you and your DS can have your own rooms.

The absolute privilege to not know any kids who share, or to airily say "you should have bought a bigger house" as though op is just a careless shopper!

Mind, I sleep in the (one and only) living room so my kids can have their own rooms, but I see that as an act of sparkling maternal generosity and frequently remind them to be grateful!

OP, you are not wrong, and everyone will survive.

Here come the mumsnet wealthy or pretend wealthy types!

Yes do you?

Do you know what 'subjective' means?

Oh apologies that should say "as was said" not "as you said" - predictive text is great at times but not always!