3 yo twins is the hardest stage. Old enough to know what they want, not old enough to be in any way shape or form reasonable. It will get easier.
Not been in your exact circumstances but have been squished and needed to carve out space for me in a crowded life.
I would say, start small. You may not have your own bedroom (and yes, I can completely see how twins change what would have been reasonable plans), but you can still carve out a bit of space for you. Do you have a favourite mug and plate? If not, maybe go out and find one in your two hours off. Doesn’t have to be expensive; a lovely teacup and saucer from a local charity shop will do. Make it yours. Keep it out of reach of the twins. And make it unattractive to your twelve year old. Mum’s cup. And when they are in bed, make yourself a cup of your favourite hot drink. Stash a packet of your favourite biscuits somewhere.
Boys in bed, you can just sit. Drink tea. Eat a biscuit. Or a piece of fruit if you’d prefer. A sugar free mint. Whatever floats your boat. Your space, your time.
Treat yourself to a fancy smelling shower gel. Or hand cream. Or a nice candle. Again, doesn’t have to be expensive. But just something which you can differentiate me time from mum time. Candles great actually, if you’re sleeping in the sitting room. They’ll hide all the clutter and chaos and reduce the pressure on you to have it all organised.
Longer term, I’d recommend a sofa bed which folds away with the bed made up. It’s miserable having to strip the bed each morning and remake it every night. And if you’re like me, you’ll not bother, and your bed will be out all day and become trampoline and den and everything else. If that’s not in the budget, then see if you can stretch to an extra large throw which will cover it all up during the day at least and which you can whip off at bedtime. Again. Less jam and stickiness all over your sheets.
Others have said it best about being ruthless over toys and clutter and chaos. Budget and rental means you’re limited in what storage you can add. But have a look at what space you do have. If you currently have a dining table, is there space for boxes underneath it for the twins’ toys? Or drawers for your clothes? Or with a long tablecloth you’ve got a fine sensory den for them to nest into if that’s what they need too.
Agree big time with posters who said try to be an outdoorsy family if you can. Certainly get them out for a run each day if you can bear to. Get them into the habit of running and jumping and bouncing outside, so that inside becomes the place for calmer behaviour. Not easy, not always possible. But if you can get that going, it will help with the feel inside too. And it’ll get sunlight on all of you, which will help with mental and physical health.
If you don’t have any outside space attached to the flat, see if you can grow something on a windowsill. Mustard and cress will grow on a sheet of damp kitchen roll or in an empty egg carton. Or a houseplant in a little pot. Something green. Something alive. Something to bring hope.
Don’t need to know the reasons why one of your twins might not manage 30 hours (or where you live, or anything else really!). But since you mentioned it, so check that you are claiming everything you might he entitled to - if there’s a chance he might qualify for dla that would not only bring a little more into the mix but could potentially open the door for other benefits too, as well as bumping you up the council house list if medically appropriate. Also there should be early years funding for nursery to give him additional support, if it is more a case of nursery not coping with him than him not coping with nursery. All of which may be completely irrelevant so apologies if that’s inappropriate. If he does have additional needs then your 12 yo might be able to tap into some young carers support too, although that varies hugely area by area. Locally, it means they periodically buy all teen carers a new bike or skateboard or similar and then vanish for another 11.5 months. Still. Better than nothing.
This won’t be how it is forever. And there will come a time when you can look back on it and wonder how on Earth you ever got through it. But you will muddle through. And it will be ok. And your boys will know you did everything you could for them.
But in the meantime, go and claim that teacup. Make a little space for you in the eye of the storm.