So, now the school term is over and this is week 1 of the holidays (Scotland here).
DS1 4.11 (HF ASD) has been getting progressively more tantrummy in the last feweeks, is exhausted, and is now exhibiting violent behaviour towards his brother (3.4) and even his new baby brother who is only a few weeks old

DS1 has always been a gentle, kind, affectionate little boy, but the ASD symptoms have been more and more evident since he started nursery.
For the past 10 months or so he has been hitting himself when at home, however now he has stopped this and replaced this behaviour with attacks on his brother - hitting, pinching, biting, and even stamping on his face 
Last summer I found his behaviour drastically improved, but the problem behaviour was more to do with getting dressed and out of the house (this could take a few hours on a bad day) and getting him to his nursery (different one) which he had developed a phobia of (due to the large room).
He is the model child at nursery, but because he is so well behaved, quiet, and nice
the staff do not recognise his ASD - despite having letters from Dev Paed confirming this as a diagnosis
. They are not meeting his needs IMO and I am concerned about the outlook for him as he goes into P1. His ASD is very invisible IFSWIM, no outward physical symptoms etc. Staff assure me there are no problems and he is not stressed. They are unable to understand that he keeps a lid on it at nursery, and explodes at home.
Interestingly, he has been threatened with losing his school place several times so far on the grounds of his poor timekeeping, and also poor attendance (despite having good attendance... 
Now that he is older, his behaviour in spare time is awful. He has violent outbursts several times a day, and I am not only concerned about this behaviour in itself, but about the effect it is having on his 2 brothers - DS2 is constantly crying and saying he is very very sad
and obviously I have to protect DS3 from attacks and also excessive affection - squeezing, hugging which gets a bit too much.
I can't ignore these outbursts as they involve others - if I could this would be an effective tool though, I used to do this but as he is now so aggressive it isn't appropriate at the moment.
I can't use time out as he is terrified of being alone (even going into another room to get clothes, go to toilet elicits panic in him). Naughty step is a source of major distress, and isn't appropriate either 
What can I do? This is just awful. He is trashing the living room and snatching toys as I speak. I can't separate them, I have no family or outside help at all and DP is away 14 hours a day at work.
Can I hope that this will improve during the holidays due to the stressor of nursery no longer being the root cause? This is week 1 - is it realistic to assume that this behaviour is an avalanche of post stress stress IYSWIM?
Ultimately, I am failing as a parent - I do not know how to effectively discipline DS1, or to prevent these outbursts, so I am not protecting DS2 (although DS3 is ultra velcro baby, and I even take him to toilet with me just in case).
Everyone in the house has a nasty cold too - I think this is contributing to things too