i appreciate my MIL but….

I’m not sure how and what is the tone of your husband’s side calling ‘mama’. It could be your husband family’s dialect practice so it has been like this all along and you’re not used to it since you are not brought up this way, and it’s understandable. Also, it is less known since our generation do not really know the proper traditional way of addressing/calling elderlies and relatives nowadays too. My grandma was a Peranakan and we addressed her as Má-mà since young but it is different tone from Mā-mā (mother). While I called my grandfather as gong gong. I have people always asking me why I am calling my grandmother as Ma-Ma but it’s a different tone. It does not mean ‘mother’. From my understanding, Cantonese is also called as Maa-Maa 嫲嫲 for paternal grandmother.