Another bedroom one. Disagree with DH, AIBU?

Surely they have the whole house? It's their permanent home. Equality is not the same as equity.

Any way to put a second window into the room they currently share, OP? Then you could divide it.

Do the garden room. If you can include a small ensuite with shower, even better. You could put up security cameras with apps on your phones if concerned about safety.
Done properly with heating & insulation these cabins are lovely.
Sounds like Dsc is on board with this. Their own chill out space, play games, music, own tv etc.
Could always be turned into a home office later on. Or a "guest wing".

I would go down the garden home office / room
it would be cheaper than an extension and done right can add value to the house

my son has one in his garden it used to be the old garage and the previous owners insulated it put in electrics / mini kitchen / water and sliding doors and skylights and it’s really nice apart from being to hot / cold
they use it for guest and extra space

however if you don’t have a back access to the garden about how your going to get it in and any ground work that needs to be done

my sons neighbor is doing a garden room and they have had to remove loads of soil and had to take it through the house to remove it

That's not treating them fairly or equally. Why should the DC have to share? It's their only space.

Lots of people talk about ‘going to uni’ as if the bedroom was no longer needed thereafter. DSS2 ‘s Oxford terms were each eight weeks, a total of 24wks so still home more than 50%

By not providing their own room, you are sending a message they they are tolerated rather than wanted as, yes, you will see them less and less.

that may be what OP is angling for, let’s hope their father (and siblings) have another view.

short term I would convert the stand alone sitting room and stop the DC using it when DSSs are not around or it will not feel like their own space as the younger ones will forget and burst in when he is there.

not ideal, but I agree that it will very much determine your relationship with them. Don’t try and alienate them, please.

Simple solution. Put your DC into the large room and give the DSC the two smaller bedrooms. This is fair. 3 days a week is a large chunk of the week and your DC are young enough to share. In a couple of years DSC will cease to come every week because they are older and have other things to do and at that point your DC can have separate rooms.
It's necessary to treat the DC equally, which means the older DC get separate rooms. Really, you need a 5 bed house - you could move perhaps or possibly extend downstairs?

Could you not just have your children share when they stay so that they can have their own space ?

we have a 3 bed . My 2 DC ( same sex ) are 12 and 18. My DSC is 15. When they were younger mine shared and SC had their own room . SC used to stay on a regular basis. As they all grew it became impractical for my DC to share and SC only came on weekends which has now changed to every few weeks ( at the age of 15 SC has friends near where they live with Mum and prefers to be there so they can see their friends , which is understandable ) so now , when SC stays my DC share a room. We spoke with SC about this , they understood , all things are at their Mums anyway and any clothes etc we bought ended up going back because they wanted to wear / use them more than the times they were here .

It works well for us . Maybe that could be an option ?

YANBU to not want to spend loads on an extra room because in all honesty at their age , it’s likely they will come less and less when they’re older if Mums is their ‘main’ home.

This is a difficult one. But I do mostly agree with the OP. If the step children are older teens then realistically this is only going to be an issue for another few years. If they were younger then I would say something needs to change and it would be worth spending the money. But there's no point spending lots of money and time making a 5th bedroom if you don't actually need it. And at the end of the day, it sounds like you can't afford it if it would eat up all your savings.
When I turned 18 I didn't have a bedroom at my mum's OR my dad's. Once I went off to uni I slept on a sofa bed when I did stay over.

You could split the window in two (and enlarge it if necessary) and put a dividing stud in for far less than the loft conversion. Or that bed arrangement upthread is amazing. You could make it teen aspirational with built in tech etc.

I had a small room when I was a teen and I actually really loved it, it was like a cocoon.

Yes, I agree. They're in the house part of the time, I genuinely don't know what's wrong with sharing a bedroom. I wouldn't go to the trouble and expense of re- configuring/extending a house when it's unnecessary.

How os not equal? They don’t there?

Knocking another window in the big bedroom to properly partition it would likely to cheaper than a loft conversion?

I would certainly consider the loft conversion. Yes it would cost, but would add more value to your house than your suggestion of landscaping the garden for example. The SC are of an age when they are, or will be , studying for exams and a decent space to do that is important, especially since they spend three nights with you.

@Georgey0 why don’t you and DH swap bedrooms with them and partition the master bedroom into two rooms for step DC. Sounds like you have the biggest bedroom and given it’s a master bedroom, there might be two windows meaning both partitions would have natural daylight.

Any chance you can add another window? If it’s on an outside wall it’d surely be cheaper than a loft conversion.

There's plenty of threads where step children try and explain how shit it is but they generally get ignored. Maybe that's why you haven't seen them

for a start, does me being a step-child counts?
Not that I am pretending to represent all the step-children, but you asked.

I am seeing more angry and bitter ex on these threads , angry against the new wife, than step-kids with complaints.

I can see both sides tbh BUT overall I think do the loft conversion. You do sound (to my ears) a weeny bit resentful of the DSCs and this maybe what your husband is trying to compensate for.

It seems OP just doesn't want to spend all of her savings on it, I'm sure if DH was willing to pay for a room for his children she wouldn't mind. Can't blame her, I wonder if a woman posted saying her husband was hesitant to clear out his account to pay for a loft conversion people would say he just had to suck it up. Can guess the answers!

but the broken home is done. You might think people staying together and living in a toxic and angry house is best, I don't agree.

Once the split is done, people manage in the best way they can. OF COURSE things will be different because one child has 2 homes, and one child has one home. It doesn't mean one child is seen as superior or inferior.

Up to the adult to stop pretending difference means treating them less well.

Celebrating twice is not a compensation for parents spliting up, it's a fact proving that there will be difference. Trying to put a judgement of value on these differences is ridiculous.

Have you any experience of being a step child? Any at all?

I would absolutely not do this.

Can't even being to imagine the fall out if you give them their own rooms at the expense of children who live their full time, only to then take their rooms away from them 'for not staying more'? All planned out in advance to do it this way, too...

Or, say it works ... now you have a boy/girl sharing which isn't sustainable for much longer.

I would split the room with a clever use of bunk beds with many examples online.

"treating the same" is a ridiculous concept. It doesn't even work with your own children living together!

You adapt based on need, personality, age and it's a very normal thing to do. It's children, not robots.

On the basis of "treating the same", are you suggesting to stop celebrating their birthday if they already had one with their mum, as "treating the same" means every child celebrate their birthday once? How ridiculous would that be.

Celebrating stuff twice does not make up for the fact that they're from a broken home.

That's incredibly shallow thinking.