11yr Old jaw swinging and eyes twitching - need advice

My brother 11M constantly swings his jaw and moves his eyes to the left whenever he talks or is just sitting down doing nothing and I'm wondering what it could be? In the past, just before these new actions he would constantly be straining his eyes to be looking up and before then I remember he also had some other form of similar repetitive actions he would act out until they stopped. All of which he seems unaware of.

Whenever he talks as well he always has to clear his throat in between most words and usually repeats the first syllable of most words almost like a "stammer" eventhough he has no cold or any throat issues right now. This "stammer" thing has been a thing for many years as far as I'm aware.

In addition to this, ever since he has learnt how to whistle properly, he can't stop whistling even when I have told him to stop. I know I can just brush that as a child who is being naughty but I genuinly don't think that's the cause. I have asked him why he does all this and he says he doesn't know. I am aware of tics and torettes where you get involuntary actions so I asked him if he can control it or if he is aware these things r happening and he just says "I don't know i guess"

All of the things mentioned above doesn't seem to be causing him distress tho as I've said before he doesn't seem to be aware of any of these things happening.

Another thing to add, I strongly suspect my brother does have ADHD so I'm not sure if that may explain some of the issues. He also has an inhaler he takes for his asthma but other than that no other medical conditions

The reason I'm here is because our parents don't believe anything is wrong so I am unable to take him to the GP to get it seen so i am just asking for more input from this subreddit on how I can possibly go about this to finially get him seen by a doctor.