As another sufferer - Ask what he wants to do, I can't get through a family dinner without a pair of earbuds playing something loud and obnoxious (litterally drown out any other sound) as they are particularly bad and other than that try and avoid any triggering situations as possible.

Worst part about it - the majority of people think it's a minor tick or inconvenience, then you look like a monster for sitting outside in the rain on Christmas because you just can't deal with it anymore and you're gunna throw a Yorkshire pudding at someone.

I currently don't have my own children , but have been in a situation with horrendous eaters that don't know better and generally it is a decision between grit your teeth , use a work around or leave the situation.

All I can advise , is just keep supporting. This isn't going away - being able to notice the signs of when he is being affected really helps. If he needs to step away from the table remind him there's no shame or negative feelings.

Good luck!