I would say practice, practice, practice respecting people's personal space. Reiterate with him whenever possible that everyone needs their personal space and we shouldn't invade other peoples' space unless they invite us to do so e.g. "can I have a hug?"
It is fairly common for kids with ASDs to show inappropriate responses such as laughing when you are angry with them. It is most likely (especially at 4) not intended to make you even more angry, he probably can't really help that his emotional response comes out as a laugh. I tend to walk away or otherwise ignore it when my 5 yo does this. It can feel so infuriating to me then I remind myself that he isn't trying to push my buttons its just how it comes out for him.
Don't hesitate to tell other people to remind him not to touch them without permission. Even, if you can, teach little sister to stick up for herself (I don't know her age but maybe you can work on this with her). The more he is reminded that touching other people without permission is inappropriate, the sooner it will sink in for him.
We have a general rule at our house that there is no "shooting" at each other. It almost always ends in screaming fits so I just put a stop to it and suggest a different way to play together.
