Tremendous advice here, thank you all.
"she accepts he is at work, but thinks seeing her should be prioritised over his job, even if it means risking being fired, being demoted, not being able to afford to keep a roof over the heads of his DCs, the priority should be her happiness. Telling her that he's busy at work might mean she'll accept that he is busy at work, but that won't change her view that the shouldn't be too busy to see her. Heck, if he was a good son, he'd get a different job, one when he'd be free when his mother wanted him, right?"
Dinosaurs - this is spot on. Seeing it written there in black and white helps me to realise that it IS unreasonable. DH is about to be promoted to a very senior role, one that he has wanted his whole life, and it will clearly give him a different status. He thinks this might 'sort the problem'. I'm with you - I don't think it will.
They often say things like 'No-one loves you like family, family are the most important thing, we want to see you'. Which, on the face of it, is lovely. But when we do meet with them, that is exactly what they DON'T do - they DON'T 'see' us. They don't listen, they don't hear what we are saying, they don't even ask if we are OK (there is absolutely no talk of emotions, ever). Instead, they bully us to make us 'fit' into their template of what they want to do, and who they want us to be. 'We' don't actually figure at all, not as independent adults, anyway. We could be smiling robots touring three National Trust properties a day with them and they would be just as happy. (I bloody hate stately homes).They don't even seem aware of us as people with basic needs, e.g. to sleep. Last visit, DH was particularly tired, and I made a point of mentioning this. They still managed to wake us at 2am (FIL knocking on our bedroom door to ask if the front door was locked) and again at 5am (MIL talking at the top of her voice to the cat right outside the bedroom door).
DH is absolutely mired in the FOG. The first thing everyone says about him is 'He's a lovely guy' - because he'll bend over backwards to help people. To him, they are 'loving' parents and he is a 'bad' son for not doing exactly what they ask at all times. Yet they have damaged him so much. For years and years and years he thought he was incapable of having a relationship, that he was rubbish, uncaring and bad at building bonds with others. Even though we are married, I know a part of him still believes that because whenever anyone asks him for something - however unreasonable - he feels miserable if he can't deliver.
He and his brother both believe that PIL 'mean well' and are 'lovely really'. I would never stand in the way of their relationship by asking to go NC or anything. But I don't agree - I think they are selfish to the core and that they don't 'love' their children in a healthy way. I would never dream of asking DH to go no contact with them (I don't believe he could actually), but their behaviour is not normal!!