But your total lack of empathy towards any possible issue for your DH is a little concerning
That was my impression too reading through your posts, OP. You've called your DH a fuckwit, said you don't care how he feels & set out your expectations in a way that would certainly get my back up if my DH did it to me.
I'm sure other posters have pointed out, too, that these 6 family occasions you keep mentioning aren't just random dates, are they, they're major holidays that you assume have to be spent with your family EVERY SINGLE YEAR. That would drive me insane. It sounds like it drives your husband insane. Why doesn't that matter to you? Doesn't he get a say at all?
OTOH I do agree that hosting your MIL for 9 weeks goes way beyond the call of duty, & that your DH's timing in voicing his complaints - just after she's gone - makes him sound fecking ungrateful. Have you discussed with him the apparent mismatch between what he wants from you, in terms of hospitality to his family, & what he's prepared to give?
At the end of the day, though, even if you have had his mum on an extended visit, I don't think it's fair for one person in a marriage to get the final say about days like Christmas, Boxing Day & Easter every single year. And I don't get what there is to be gained from trying to insist that another adult attends certain social events when they clearly don't want to.