To think 7yo deliberately hurting 2yo is not normal?

Calling him psychopathic is hardly helpful. He is a product of his up bringing. At 7 he needs help and understanding, not written of FFS.

Sorry but he does sound psychopathic and dangerous. Just because he's possibly ND doesn't make it any more justified or deserving of sympathy. There are thousands of autistic/ADHD boys who don't wilfully harm their siblings.

Every dangerous adult had warning signs when they were children. 1 out of 5 men are abusive and he's probably going to become one of those when he grows up. That's the best case scenario. Worst case scenario he'll end up in jail for some violent crime.

There is a cousin in our family who displayed similar behaviour from a young age. Diagnosed ADHD and medicated but the issues still come and go. DH and I have basically agreed never to let our kids out of sight when this cousin is around. He can be great 95% of the time but suddenly lash out without warning and become violent before adults even have the chance to intervene. It's really not worth having your own child in the firing line just because you think some other badly parented kid deserves more understanding and patience.

I suggested earlier that his Dad maybe picked him up mid week to do an activity with him. But then I realised hes an hour and half away so that doesn't really work.

Would his Mum be happy for him to have an hours gaming online with Dad once a week?

Or on the weekends he's not with you Dad go get him and do something with him, especially if the boy is going to be with babysitters.

It sounds like there is a biggish age gap between him and his full sister's and again with the two half sisters.

Its probably impossible to find things to do that are age and interest appropriate for all the kids.

He's middle at both houses.
He has 2 full sibling sisters who are older than him.
And 2 half sibling sisters, one in each house.

'I don’t think he has autism personally, I think he’s the product of his environment: little consistency or structure, far too much screen time, multiple caregivers from the start, and busy households. I do suspect ADHD'

I had similar thoughts. Plus he's the youngest at one house, expected to be oldest in another. Approaching school for extra support and documenting your concerns re his behaviour with DD (with school and/or GP) may be your only option. I understand what you say about being a product of environment, but his behaviour is putting her at risk.

Its a combination of things.
Getting to the root of his problem will help understand and stop the bad behaviour.

It really sounds like he is struggling badly between two houses, two sets of rules, babysitters and the stepdad trying to give him 121 time, but reality is he'll be wanting 121 with his mum or dad.

Sounds like everyone its trying but not singing from the same hymn sheet, just confusing and upsetting him even more

Late to this thread as ever but had to jump on. OP, your SS sounds very much like mine, in many ways. Mine is 14 now but would have been very much like this at 7. He is almost certainly ADHD, likely autistic and probably FAS too.
I hate to be the voice of doom, but things are no better now than they were at 7. In many ways they’re much worse. I had a thread a few months back that you can find on advanced search if you like. I think your concerns about what happens when SS’s hormones kick in are very valid. I have very similar worries. My SS presents as engaging and chatty, and on a superficial level he is likeable, but I think he is absolutely without empathy. He’s learnt the right things to say, but he doesn’t care at all when he hurts or upsets someone (which happens on a regular basis) so nothing ever changes and so we just go round in circles.
Everyone on my thread said to move out. I feel for you as when you share a child there’s no good option either way. I haven’t moved out, but what that means is I feel uncomfortable in my own house pretty much all the time as SS is with us 100% of the time. It’s royally shit living with someone I don’t trust and, at this point, don’t even particularly like. We have social services involvement thanks to SS; there’s no concerns re parenting so we are very much working with them and they’ve actually been brilliant, really supportive and have opened doors of support that we didn’t previously have access to, so it hasn’t been all bad - but the fact that my children are on their radar in the first place thanks to his actions makes me so angry I can hardly look at him most of the time, much less engage with him. The rest of the blend is lovely and really happy despite being complicated. I adore my OH, my DSD and our shared DC but if I could go back in time with a crystal ball I’d never have moved in with OH as SS has made our (mine and my existing DC)’s lives so, so much worse.
Like I said I don’t want to be the voice of doom but I’d think really carefully about how you move forward from here. Your situation is a bit different as you have your SC so much less so at least you have a break so it’s probably worth sticking it out, but I’d get things in place to be able to separate yourself and your DD from SC. That’s what I’ve done - I’ve essentially unblended me & mine from SS, which is horrible and makes me feel so guilty, but ultimately I have to put my own DC first. They’ve come second to SS’s wants and needs for years and it’s made no difference except damaged them and my relationship with them and I’m not willing to do it any more. Distancing myself from SS has been tough on my relationship with OH but thankfully he doesn’t hold it against me as he understands - he doesn’t enjoy parenting SS and that’s with the unconditional parental love which he has and I don’t - but that doesn’t mean it’s always easy for me to hold the boundaries.
Much of what you’ve posted could have been me a few years ago - and I wish I’d made different choices then. You can rip the plaster off now and find a better way forward for yourself and your DD, or you can spend the next however many years stuck in the same place. And in five years’ time when nothing has changed except that you’ve gained anger and resentment and you feel like you’ve been cheated of your DD’s childhood, you’ll look back and wish you’d done it now. And I know this because I feel exactly that way and it sucks. I can’t get the time back but I can change things moving forward, make the most of the next phase and show my kids that they come first and their lives don’t have to be smaller because of a situation they never chose and that I never meant to inflict on them.

Whether the ss is on the spectrum or not, or has problems due to a dysfunctional background, is a red herring as far as OP is concerned. Her priority is her child and their safety. Many kids have divorced parents but don’t do the horrific things this lad is doing (dropping child on concrete, for example). Yes, the SS needs to have help and support, but for op, that should be a secondary concern, after the welfare of her child.

I think a prime reason for diagnosis is that it helps everyone understand him better (and will help him understand himself better as he gets older). Plus if you know exactly what you're dealing with you're more likely to look for support/advice in the right places. There's no point asking parents of NT children how they deal with x as it may well be very different to how parents of an ND child will deal with it. A prime example would be have you considered his rough play/getting too close to people could be a sensory seeking behaviour? NT parents will just say punish him, it won't work. ND parents might suggest a sensory occupational therapy assessment or advise on things that regulate their child with similar sensory seeking behaviours, which are far more likely to make a difference for you all.

What an absolutely vile comment. His behaviour is unacceptable obviously, and worrying but its pretty obvious from OPs update about his siblings why its happening. New siblings at mums house, new siblings at dad's, older siblings no time for him. He needs some one on one time with both his actual parents, suitable activities to engage him and possibly for everyone to stop having more kids. 🙄

@Xante Just wanted to say that you are a lovely person caring for this boy even though he's hurt your dd.

It isn't a tick box exercise. So one child I work with makes eye contact (and will stare at you intently), is the most able child in the class, eats well (however this is a set packed lunch of specific items), usually sleeps well. They are however clumsy, and they prefer to play alone. They struggle with social interactions, will snatch off others if they want something and need an adult to supervise them.

Being diagnosed might give him time with an adult at school within the classroom, or to access time with an adult to develop other social skills, even in a small group. TAs sometimes take children out to work on this e.g. playing a simple game to understand turn taking, winning and losing.

@Xante I have been reading from the start of your thread but haven't commented...but I really want to send you some kind thoughts, you are so considered in your approach to this and your SS is lucky to have you in his corner.
I am horrified by some of the comments on this thread.
Keep strong.

That type of conversation is held by someone who is storing up evidence to use against you later. Repeated confirmation, verification and consent. If it doesn’t rain, you will be held accountable

Leave him by the side of the road and run

Agree. That sounds exactly like the type of conversations I have with my autistic child. Also the lack of awareness of personal space and physical roughness to get attention.

That type of conversation is very typical of a child with autism in my class. Repetitive checking behaviour.

I don't expect anything 😂

I like how you swerved the other question.

Yes but does absolutely nothing to help SS

Which btw is your partners duty.

How long are you together?