The picture system is often based on PECS - picture exchange communication system. It works through different levels and usually is started by a Sppech & Language therapist; good that you're getting a referral.
I teach children with additional needs and have used similar systems. Pictures can present challenges initially as the child has to make the link between the picture and their thing which may or may not be the same. This type of system therefore often starts with concrete (real) objects, then photos of real objects and finally pictures.
With regard to other childre, I'm not a mum myself and never preach to parents as I don't know what parenting is like at any level. What I sometimes think happens s as you say, other kids end up taking on a caring role which is hard. My thinking would be if your son is intelligent, cheeky and lively, then treat him as you would your other kids if he behaves badly. It's okay to be frustrated angry, but it's not okay to hurt others or damage things. I think the key here is to decide what's acceptable to you as parents, and what you will do f the behaviour occurs. Then you implement this consistently again and again. Be prepared to weather the storm initially - it can be hard, but ideally within a couple of weeks you should see an improvement. If not, back to the drawing board
Something else you can try if he's able in understanding is Social Stories. It may be a bit early for this, but essentially they explain what happens, how others feel, what you would like instead, and finally how people feel then. This is very vague - there's lots more behind it, and if you google this and Carol Gray you'll get more info. I've used them successfully with quite a few kids. They were designed for kids with autism but work well for others. Again, the key is in the repetition and getting the message through when a child is calm.