I’m just waiting for someone to suggest you book a spa day. Perhaps you could take your cleaner with you as a treat 🙄
Your partner is not just as busy and just as tired. It’s not him cutting up bits of card late at night, is it? He’s not worrying about a mental load.
Household rota. The DC might be too young to cook, but if they’re in primary, they’re old enough to tidy. You and partner take turns cooking and washing up so each of you get a night off a few times a week. Give him back the responsibility for half of the housework. If the DC don’t stick to it, they lose privileges. If your partner doesn’t stick to it, or he purposely fucks it up so you take over and don’t ask him again, then he can fuck off and find himself another housekeeper, cook and chief bottle washer. You’ve already got 2 kids, you don’t need a third. If he doesn’t like it, point out that he’ll have to do 100% of the housework when you finally snap and throw him out. And don’t ask for his ‘help’. He is not helping you by changing your DC’s beds. He’s doing his share. Helping you would be running you a bubble bath and putting towels on the radiator to warm up. Bet he never does that either.
And start saying no to stuff. If your kids come home saying they need this or need that, you write a quick note to the teacher saying you’re not able to help but will reassess the situation in the future.
If family is demanding your time, the only answer is ‘No, I’m running on fumes, I can’t do it’ If you fall out with them, then so what?
And let things slide a bit. Things don’t need to be immaculate at home. Christmas doesn’t need to be perfect. Channel your inner ‘Fuck it’ for a while.
What you’re doing now is not sustainable. You are not responsible for everyone and everything.