People are saying get him to cook once a week etc, but that's not what is causing the problem from what I can see.
I have direct experience of this as a sibling, a spouse and a parent.
Your son is capable enough to have a job and run a car. Yes he has a disability and possibly he's masking in work all day and that's why the pacing and clicking of a night.
I agree with other posters about sitting down with him. I'd give two options.
- Move out. Then he can behave exactly how he wishes. You will still support him where needed, invite him round for meals, on days out with the family etc.
- He makes some changes which should then help his behaviour. The biggest I can see is him doing something high energy straight from work - box fit, jujitsu, climbing are great for ADHD due to the release and also the sensory input. Also he is more likely to make friends there than at a gym.
This may then help with his pacing and also his winding up of siblings because he's had his energy release and dopamine fix. Also would get him out of the house.
Are there other activities he could do than the pacing and clicking? Kinetic sand, lego - things that keep his hands busy and give him sensory input.
Look into sensory circuits. They're used for children a lot but can be adapted for adults. They're activities done in a certain way to calm the body and mind. They may help him to decompress and regulate himself.
Has he disclosed his condition at work? They could make adjustments like allowing movement breaks. If his job is sedentary, maybe more active job may help.
Could you and your husband come to an agreement where you alternate nights to relax in your room of a night so he has a night in his room watching tv etc and then a night where he can pace workout bothering anyone.
Loop ear plugs could be helpful for other members of the household when he is particularly loud.
Have a look into rejection sensitive disphoria. This may shine a loght on his reactions and help you to communicate with him in a more productive way.
Could your DH do an activity with him (climbing for example) so they bond a little rather than constant negativity.
I don't blame your DH. It's hard loving with someone with ADHD and it's his home too. Same as your other children. This could end up in them moving out as soon as they can and being resentful of their sibling. You have to think of everyone, including yourself and your son. I don't envy you.
As I said, I have a lot of experience in this area from all angles. If I can be of any help please PM me. I hope some of this is helpful to you.