Hitting, throwing things and hair pulling

I’m looking for some advice, please and would be very grateful for insights.

My son, who is 3, is waiting for a diagnosis but the paediatrician said ASD/ASC is what they’re probably looking at. We are struggling to know where to reach out to for help as he’s currently between portage and early years inclusion.

He is causing injury to all of us in the household and I’m not sure how to tackle it. He doesn’t respond to “no” or “stop.” He has no empathy and doesn’t understand that it’s unacceptable to hurt people. He has recently started throwing things, mainly toys, at us. His older brothers are scared to walk by him in case he throws something at him. He’s hit both of them in the face with toy cars recently as he has an incredible aim and a powerful throw. I can’t take his toy cars away as they are his obsession and has meltdowns when they’re removed. He doesn’t only throw things at people, sometimes he just throws things. He has broken two televisions by throwing toys at them. 

He has an obsession with bare skin, especially on his siblings. When I attempt to change his twin sister’s clothes, he immediately runs over to her and attempts to slap her. He doesn’t appear to be aggressive when doing this - I think he likes the sound or the feel or maybe even he wants a reaction. Sometimes he will slap her for no reason and other times he pulls her hair. There doesn’t always appear to be a reason for these behaviours. Sometimes he does lash out in aggression but we can see this coming and are quite good at preventing it but it’s hard to prevent it when it seems to come out of the blue. The other night, he slapped her while she was sleeping in bed. 

On other occasions, he can be very affectionate. He will show affection towards his twin sister - he will kiss her and hug her. She doesn’t always know what his intentions are though and is wary of letting him near her.

His communication isn’t advanced enough for me to ask why he’s doing these things. Sometimes he will say sorry afterwards but I’m not sure he really understands what that means, I think he just knows when he’s supposed to say it. 

As an aside, I’ve applied for social housing to try and provide a separate bedroom for him and his twin as I feel so sorry for her that she’s having to put up with random and unprovoked physical attacks but unfortunately I can’t keep them separate 24/7 and at present there’s nowhere else for her to sleep. In the daytime, we try and keep them separated but this involves his twin sister being in the kitchen and another adult has to be present to make sure she’s safe.