Some kids are just really wild by temperament and it shows up in their first year or two on the Earth.

Short of breaking their spirit there's not much the parents can do to make them less wild. Parents have to try to find a way to let the kid be wild and feel good about being a temperamentally wild kid while also recognizing that there are limits and boundaries. A similar experience is perhaps owning a dog that needs to run around outside every day.

But nothing in the autism or ADHD diagnoses says you can't learn social skills or that they shouldn't. Nor does it require anyone to endure abuse or physical attacks.

Assuming you're not the parent (since you say the more generic "family member"), probably the best thing you can do is try to befriend this kid and learn a bit about what's like to be them. And try to find traits in yourself that help you see why they act one way or another.

Another thing to keep in mind is that things you take for granted may be very distressing to this person. They may be able to hear noises or smell smells or taste flavors that you can't. The parents have a tough job because nobody wants their kid's preferences to dictate everything, but nobody wants to knowingly make their kid distressed when they can help it. That becomes a tough tradeoff when you have someone who is easily distressed by a world that isn't really designed with their brains in mind. This is where things like earplugs and sunglasses can help. It's a bit like being hungover all the time. If you reduce the sensory input everyone becomes less irritable and more even keel.