This is far from usual.
DH and I (and the children) get on really well with both sets of parents, who are easy going and a pleasure to be around.
We see them once a month for an afternoon and every 4 months or so overnight (for one night). Granted we live within 2 hours radius but if it was a longer distance the set up wouldn't change all that much.
We are in regular contact by phone/text.
There is no way I'd host my parents or in-laws for a week every month/6 weeks or spend every school holiday with them.
I'm interested to understand how much does your DH help with hosting? Is he cleaning rooms/bedding? Doing the additional cooking/shopping?
Also where do your family fit into this? What space is there to see family other than his?
He's right that they are family too...but you and his children are now his primary family unit. That's the priority.
I can't fathom his thinking. Is he being bullied into this by his parents and making this your problem to make you the bad cop?
Or is he still tied to the apron strings? You say they can be difficult- does he actually enjoy having them to stay? When they do does he spend more time with them than you and the children?
How does it play out when they visit? Does he spend time with his family/all together or bugger off elsewhere leaving you to deal with everything?
Upshot is it's not just his home. It's yours and the children's too. His "say" isn't final.
I'd think about what you think is reasonable and stick to that as a boundary.
If he won't agree then I'd down tools and make clear that every aspect of hosting his parents (from making a cup of tea to full meals/cleaning rooms) is his responsibility.
I'd do my own thing when they visited, including with the children.
I'm not sure if he's selfish or weak (maybe both) but his actions are very unattractive in a partner.
I'd make that clear and suggest that if he likes their company so much maybe he'd like to move back home like a manchild because he'll have to revisit his current accommodation post divorce.