Sorry I haven’t replied to your post sooner - I have a lot happening at the moment.
Your boy has such a lot going on doesn’t it; he has lost his Mum, is living through a pandemic and now he is in year 6 and has the enormous change of secondary transfer to prepare. Also, although he is only 10 years old, many children with special needs have ‘precocious puberty’ - puberty that starts early and those hormones create havoc.
Is he holding it together at school apart from playtimes? If so, then the structured playtimes, when certain peers are winding him up, will certainly help. Does he have a ‘safe place’ to go in school when he is feeling wound up or anxious? I know you asked primarily about supporting him and managing his behaviour at home and your house, but stress from school adds up and if he is holding it together in school - then it he is more likely to explode at home.
Does he have an EHCP? If he and his Dad liked the special school, then the educational psychologist and any other professionals involved need to state that he needs a special school placement on the EHCP and school need to start evidencing why. If the local state funded special schools are full, then the LA have ‘look creatively’ at finding him a place. This means funding an independent school if they cannot provide him with a place in a state one.
Ok, back to home life. It’s great that he is having the counselling and that should help (is the person experienced in supporting people with autism?) Just one more question does your boy know he has autism?
How hands on was his Daddy before you lost your daughter? She probably had all manner of tricks and strategies in place that helped manage his anxiety. His Dad or you might benefit from a Cygnet course or similar which provides lots of autism specific strategies, and a chance to talk to other family’s dealing with the same issues. The SENCO should be able to find out if there are any locally.
Routine is as you know so important also lower demands (but don’t lose them altogether). Note what is triggering him at home so this can be avoided wherever possible. What are the warning signs before he blows? Spotting the early signs is really helpful as then he can be redirected before its too late.
When S was in his early teens he went from being a passive boy who coped well as long as autism strategies were in place to unpredictable, highly anxious, angry, lashing out and breaking things. It was a scary time. I turned our study/old play room into a relaxing room for him. Blackout blinds (as he calms quicker if its dark), a second hand crash mat, big beanbags, big gym ball and a soft plastic bucket with various fidget toys in that he could have the satisfaction of kicking over. Over time I taught him to go into the relaxing room if was getting anxious/angry and to stay there until feeling calmer. It worked for us. It needn’t be a whole room it could be a sofa in a curtained off area under the stairs or a transformed garden shed or whatever.
A referral to an occupational therapist via school or GP for a sensory assessment would be very helpful. They will assess is sensory needs and be able to plan strategies that help him self-regulate/keep calm. Often there is a wait for this. In the meantime, increase his exercise to help lower his anxiety and as an outlet for all the pent up feelings he has. Needs to be something he enjoys though - long bike rides/ running / boxercise/ gym / swimming etc