I can’t accommodate son who’s struggling, can I?

She’s “sensitive” (aka rightfully pissed off and scared at the threatening and bullying behaviour) not out of thin air. She’s “sensitive” because he’s basically doing a smidge of common assault against her, so, yeah, she gets protected over him. He can just, yknow, stop being the aggressor

It's a no from me. He doesn't respect the house or the people in it by the sound of things. It's not all about him. Instinct tells me he isn't trying his hardest to find somewhere else to live and is trying to force himself back into your house

I support your sister.

I'd have the son back only once at therapeutic dose of medication personally.

If you let him back you'll be teaching all the wrong lessons to the 3 DC. I have an aggressive difficult brother and my DM never stood up for me. In fact, she never stood up for me against anyone, and I keep that in mind when she asks me for something.

This

I think u will have to say to him No !
if the circumstances were different I would readily say yes let him come home !
my son similar age was living independently with his girlfriend and they split up he could rent by himself but he was struggling with a breakup and felt isolated out of town so we said come home where we can make sure he is ok BUT he is independent and does respect our house ! (He cooks and washes ect )
if he was described like your son I would say No and I would help steer him in the right direction and he needs to learn actions have consequences eg burn carpet ect and how expensive things are he needs to learn to stand on his own two feet u can still be a fabulous support for him but in a way he ends up being independent ! Hope this helps ❤️

I do have some experience of this, so understand how hard it is. My nephew is now barely functioning in his own home, cannot manage money and is in a real mess. But my dsis won't have him back (no judgement from me about that, it's an impossible situation with him).

Would your son respond to you allowing him to return, but on your terms? So, a list of 'red lines' and explicit rules, one of which is that he moves into wherever there is room for him, he doesn't get to move back into his old room. If he breaks any of your rules, you'll help him move back out. You could also do it only a temporary basis perhaps, state that you're doing it to support him to get back on track, but it's time limited.

Thanks, but does he have an Autism diagnosis, or do you suspect it?

I accept you can't have him at home, so how to solve it? Has he ever been for a diagnosis?
A diagnosis resulting in benefits would make a huge difference to his life.

His sisters are children being intimidated and subjected to physical violence. OP's son clearly needs support but her younger children need safeguarding against this behaviour. He is 25 and whilst I know autism is a disability and affects the individual's ability to manage situations and live independently, he needs to take ownership of his violent and aggressive behaviour and regulate himself in a different way.

Support him to find other accommodation not to come back to your house. It doesn’t sound as if it’s in anyone’s interest for that to happen.

This is such a hugely common situation with male Autistic teens. And I am not generalising that all Autistic people do this. Yet there's a huge common theme on many groups I'm part of where the boys end up punching walls, aggressive, fixed views to the detriment of others. ' jokes ' that are anything but funny.

Tbh OP, you might feel shocked by this but I'd tell him he needs to think about a consultation with a psychiatrist and consider a medication like fluoxetine. It's for depression and anxiety. It has an effect of helping manage stress. Life is stressful for ND people by it's current societal design. Stress feeds outbursts from the research and consultations I've sat in on regards this.

Your language downplays his risk emotionally at least to his sister's and you. It's not right. It feels enabling. I understand because as mums, we all do it. We do it because they're vulnerable. It isn't the right thing though. You need an in between agreement where either he gets medicated and tries to sort that shit out or he accepts your help for alternative accommodation or you're out.

the rest of the shared house is a tip and for the last few months he’s been the only tenant left and doesn’t do any housework

Did he do housework when other tenants were there?

OP, as someone who grew up with an older, domineering ND brother, I implore you to please don't take him back. He is out of the house, you may be not be able to get him to leave.

My sisters and I spent our childhood and teenage years on tenterhooks wondering when the next tirade of shouting was coming our way. He would also threaten physical aggression.

Every time we went upstairs we would check if there was chance brother was coming out of his room on to the landing.

We never relaxed in that house until the day he moved out.

Well you do really as his sister being sensitive seems more important than his diagnosed condition. You don't have to take him back, he's an adult but you need to own the fact that you dont want him back.

No you can’t have him back, he’s impacting on 4 people? It’s heartbreaking and hard but I think in this case tough live is the only way forward.

I would also agree with posters who say that having him move home again is not a good idea for all the reasons you have outlined. You are going to have to be kind but tough and be firm that that is not an option [and nor is he going to live homeless in his car on your driveway.]
So,
Adult social services - what are the support options? Are there any training options to reskill - it doesn't sound like it is all about housing.
Help him look for a new room and if needs be help with temporary financial support
Help him look for a new job that comes with housing [and might mean he doesn't need a car?]. What does he actually do? Has he got transferrable skills to something that might suit him better since he hates his job too.
Is he a good driver? Long qualified? Could he train as a lorry driver or farm heavy machinery driver for example?

Then there's the social aspect, the aggressiveness, the hoarding and carelessness. Can adult social care help with teaching him some of these skills so he can sustain housing and learn to live with other people?

I would quibble a bit with that. Him being an adult, with a job and wage means that he has choices that her younger two children currently do not.

Loving and wanting to support all of your children doesn't diminish with age, I agree, but OP does have to consider her minor (female) children somewhat differently to their adult brother because they have absolutely no reasonable ability to escape whatever family environment she chooses to put them in.

I would argue that she therefore owes them more responsibly and consideration in this particular circumstance and he should not be allowed to move back in and make their lives considerably (and inescapably) worse.

He’s 25! I was divorced by then and I’m only 38 now!

ETA: just seen previous poster’s edit!

He's also very young.

Edit: I misread OP as him being 18, doh.

This is eerily similar to my brother's situation right now. He's difficult. Can't hold a genuine friendship, has fallings out at work, argues about everything, knows best but REFUSES to accept his autism plays a big part. My dad recently asked him to move out for the first time (at 35). He makes his money struggles and everything that comes with it everyone else's problem. He's the victim and poor him. My dad is absolutely in a position where he can take him back, lots of spare rooms in his house, but he won't. Mainly because he's so hard to live with and makes my dad miserable when he's living there, but also because it's not good for him. He's in his mid 30's and only now paying his own bills and creating his own life. It's not the best for him, you and your husband or your daughters to take him back. Love doesn't look like giving them everything they want. Sometimes love looks mean but it's absolutely the best thing for them.
Regardless, this must be hard and you have my full sympathy.

Two things from me. You (anybody) can only give what they have got and you haven't got the facility to give him what he wants/needs. Thats sad but true. Second thing is UNDER NO CIRCUMSTANCES (unless you win massively on the Lottery) should you or your DH be a guarantor for him. Third thing (sorry) is that your other children have rights too.

Oh please. He’s a) autistic and b) male. With aggressive and slovenly tendencies and 2 sisters do you honestly think there’s a chance in hell he’s going to look after op in her dotage? There’s a difference between being messy and leaving holes in walls.

If he has no life outside work, he really only works to cover his rent and food. If you take him back, is he likely to quit work and become a permanent dependant?