ANSWER:
It is not your obligation to make his mother happy. If you do that out of your own good will, this is rewardable and a good deed.
He can’t expect you to do things that are not obliged upon you just to make him happy!
If he is happy if you don’t open your mouth and never say a word, would Islam encourage you to do so? Of course not!
https://www.assimalhakeem.net/my-motherinlaw-is-bing-vry-aggressive-and-vile-towards-me-im-not-allowd-to-sit-with-the-family-eat-with-the-family-n-also-cook-for-my-husband-or-myself-she-says-i-cant-eat-the-food-she-makes-whe/