I can't bear big family gatherings and find the whole closeness thing extremely claustrophobic and uncomfortable and gatherings boring tbh. I resent the daily intrusion into my life. Dh is very close to his family but understands that is not for me. He goes to see them whenever he wants and if I feel up to it I go. He is also uncomfortable around my family but as we aren't close geographically it means maybe seeing my side once a year.
I think six times a year for large gatherings, plus the fact that you are in daily contact, is a lot and I know I would feel that mil, sil etc were always coming first ahead of the focus of my main family unit which is oh and dcs. Perhaps he thinks you don't put your immediate family ie him and children, first?
His mil coming from overseas (Ireland?) for nine weeks might have stressed him out and he might not have wanted her to come for that long at all :) mothers can have a habit of inviting themselves round and it's hard to say no.
The problem might not actually be the family but how he sees you and his family unit interacting iyswim.
I think he is, however, expressing himself very poorly and using language which is not pleasant.
Also if your Dm does childcare then he does need to be grateful. But grateful can turn into resentful and even the childcare in itself could be seen as your family taking over everything (not saying they are but that could be the perception).
It shouldn't be tit for tat but an agreement where you both discuss your wants and reach a compromise. No he doesn't have to go to all these gatherings but yes he needs to talk about them respectfully.
I think you are understandably resentful that he has chosen to tell you in such a way without discussing it properly or giving you a chance to share your view. Do try to take a step back and consider it from his angle and ask him to do the sake for you. Hopefully there will be a middle way :)