So the person violating your son's space is 60?? So odd ! Do they have mental health issues?
You might need to be firm and ensure they are nowhere near your boy!

You need to sit down with this family member one on one and tell them what they are doing wrong. My son is 17 and will now tell people their violating his space, but he couldn't do that when he was 4. You have to be his advocate always, even with family.

I agree with Wanda111. At 60 they should get it.

Your son didn't do the wrong thing by hitting the culprit
He clearly said No and wasn't respected!
That's what happens to bullies when they don't listen

Talk to his mum firmly that this is not acceptable

By example and showing them over and over again. My oldest has autism when his baby brother was born the smell of body lotion hurt him then he would push his brother away. Then I figured it out stop using it and now they are 2. Years apart and are twins connected to the hip both have autism