What does the mum think about this set-up OP?
Because that is important here.
Is she working all day, doing a lot of childcare at home, you say the dad doesn't work and the children are in full time childcare. So I am assuming the mum is working.
Not that is it for women to sort out the behaviour of men, but there is a 6 and 3 year old in the middle of all this, why doesn't she point out that it is the dad that needs to eat where he feels comfortable? (I say this as it sounds like the dad seems to have monopolized his needs within the household).
And perhaps he does when they are alone, you only see them when there are many people around, so why he was sitting in headphones at the table instead of eating off in the kitchen is a bit of a mystery.
You can have selfish twattish parents who are NT and selfish twattish parents that are ND, that's just life and obvious, using whatever you do as an excuse is detrimental to the children you bring into this world.
There is a elevated possibility that their children are ND, so this needs to be taken into account, because as many have said, for children to mask is not a good thing. And eventually the mask will slip, if it's there. Because if their children are ND they will need patience, understanding and guidance as they go through life, there will only be so many jobs that ND adults can do, look at this dad in question, and they will be competing against other ND peers for these positions not NT adults.
You are not unreasonable to notice this, outwardly at least, selfish twattish behaviour from the adult at the dinner table, I would talk to the mum. Personally I couldn't put up with him being at off work without kids all day, then being present but zoned out at the dinner table, and what else? Bedtime too chaotic, he needs more downtime? Whilst you run around ragged because of you know "his" ND. This is part of the reason it's good for adults to get a diagnosis if they didn't in childhood, if you have a ND adult, you can make a more informed choice if you want to become a parent with them, with the increased possibility you might have ND children. Information is important especially when making the decision of having children. Hopefully adult diagnosis will gradually reduced in future because more are being diagnosed during childhood.