as grown sibling of very hyperactive sibling I can say that it was very hard to handle my sibling's inability to control themself.

It wasn't within their capability at that time. Our household went through the diets, medications, alternatives, you name it it was probably tried. My folks weren't flakey either.

I resented the amount of time necessary to deal with my sibling. I wasn't as aware of it then when we were children but now I can honestly say it was hell. We are closer in age than your son and his half brother.

I don't have any thoughts as to how to help but just thought I'd weigh in as someone who grew up with the most hyper sibling around. Wasn't easy. Wasn't fun. Even with constant discipline in supportive single parent household (pa passed away) there were many, many rough times.