My guess is that your boy is uncomfortable with the "weirdness" of the actions/noises your brother makes. When I went through therapy dog training, we did a lot of training and activities that would mimic these kinds of situations; weird movements from people, weird noises, staring, pointing, just really odd behaviors that you might see from kids, from people in nursing homes, people with dementia, etc. Dogs can have really odd reactions to those sorts of behaviors, because it's really STRANGE to them. Some dogs just let it roll off them, but some really dislike it, because it's very, very abnormal. All of that to say, there's nothing WRONG with your boy, but of course it's something you want to address.
If possible, I'd hook up with a good trainer for a training plan, and also just because it's so helpful to have a "boots on the ground" situation with someone skilled who can see exactly what you're doing, what your dog is doing, and who can sort of refine your techniques. What I would do is start with simple classical conditioning. Get Bulleit at a distance where he feels comfortable and isn't showing any behavior change, and have your brother be there. It's less likely you can change your brother's behavior (although anything you can do to reduce the pointing, etc - great!), but what you want to do is try to change Bulleit's emotional response to that behavior. I'd simply be feeding him really high value treats as soon as he is aware of your brother's presence, keep the session short, and as soon as your brother is gone, the treats stop. Slowly make the distance between them less, but what you want is for Bulleit to remain non-reactive - if he starts seeming stressed, showing any signals of that, you're moving too fast. Again, keep the sessions short, use high value food. When he sees his "trigger" (your brother), you simply feed, when the trigger disappears the food stops. Over time, his emotional response starts to change and you should be able to work closer and closer.
A really good trainer can help you with this. Time will tell whether he improves to a degree where he enjoys your brother, or simply can co-exist in the same room. It might be a situation where you train him to go to a mat and lie down so he has a safe space that's undisturbed (and hopefully your brother can understand to leave him alone if he's there?), or maybe he's okay with being loose in the area but just chooses not to interact, or maybe he'll warm up over time...hard to say at this point. But that would be my starting point, at the very least. And you really don't want him continuing to "practice" being agitated, because the more they use those brain pathways, the more hardwired they become. So while you aren't working on training, I'd prevent interaction and prevent him from getting worked up - if that means crating him in another room, or whatever it takes, you don't want him to continue building up that feeling of agitation - it'll just make it all that much harder to break.
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